Become a TFP Supporter Pool Math Forum Rules Pool School
Results 1 to 20 of 20

Thread: What phosphate ppb will precipitate calcium phosphate?

  1. Back To Top    #1

    Join Date
    Aug 2008
    Location
    Honolulu
    Posts
    429

    What phosphate ppb will precipitate calcium phosphate?

    I realize that this might be dependent on the inter-relationship of pH, calcium hardness level, and possibly the alkalinity ppm. Is there a chart that might explain these inter-relationships and where the cutoff point for orthophosphates might occur, in other words the upper limit before calcium phosphate scaling occurs? I am not at all concerned with high levels of orthophosphate as they relate to algae formation, and am in complete agreement with this forum that properly maintained chlorine, and CyA levels, adequately compensate for this.

    The reason for asking the question is that I do not wish scale to return. In chemgeek's post here he mentions the possibility of this happening:

    http://www.troublefreepool.com/phosp...8.html#p168602

    A few posts on this issue have alluded to the issue of high orthophosphates and possible staining but no definitive numbers are mentioned. They do mention very little orthophoshate is brought into the pool by wind borne sources. Additionally there are a number of internet articles describing this issue, but again no actual numbers are mentioned. Here are a few of these links:

    http://aquamagazine.com/content/post...-Deposits.aspx

    http://www.chemistry.uoc.gr/demadis/...%20chapter.pdf

    http://www.cedengineering.com/upload...0Solutions.pdf

    A little background, I had drained the pool about 6 weeks ago, and converted back to liquid chlorine from saltwater. I managed to get rid of my calcium and iron staining through a combination of AA and HP, at an HP level 2.5 times as high as I had originally used in my prior post on the subject of HP. This was far more effective on scale removal.

    Please Note Carefully: The HP procedure is extremely experimental and not recommended for "Newbies". It also will not help very much with those persons whose fill water contains iron.

    The walls once drained looked nearly as white as the day the pool was installed some 17+ years ago. Once most of the pool was drained, on bypass, there was a huge amount of both light colored, near white, and yellowish-brown fine sandy material deposited at the bottom of the pool. It looked like a little beach, going back about 6 feet on two sides and 2 feet on the narrow side around the main drain, which I assume was the scale removed. Once the pool was refilled, my suction side cleaner removed most this material to the sand filter and was backwashed out, it took 3 backwashes, over two days; the pump and filter ran for 48 hours.

    I added back Jack's Magic "Purple Stuff" at a level of 40 ppm. I now think this was a mistake, I should have added only 12 ppm, my reasoning being that most of my iron staining issues were a result of not getting rid of the underlying problem of scale. Scale, not iron, MIGHT, please note I wrote might, be better controlled with Jack's "Magenta Stuff". As this is an Acrylic Acid Copolymer, it seems from reading various sources, this is more effective at preventing scale. I have not yet added the "Magenta Stuff".

    In 6 weeks the orthophosphate level has reached around 7,500 ppb, tested with two different kits. My municipal fill water has around 400 ppb. My assumption is that most of this additional 7,100 ppb came from Jack's "Purple Stuff". Since 6 weeks ago I have added no additional "Purple Stuff", and using Jack's test kit, the sequestrant level of the "Purple Stuff" still reads 40 ppm. Had I not raised the sequestrant level to 40 ppm, and only to 12 ppm, my orthophosphates might now only be 2,130 ppb plus 400 ppm from fill water, or about 2,500 ppb.

    The pool currently has not the faintest hint of staining YET. And I would love to keep my pool scale and iron scale free in the future. Scale is even a bigger problem in Hawaii, according to Jack's tech person, than iron, but he could not explain why.

    I believe my scale problem developed many years ago before I started to balance my pool according to this and one other forum's recommendation. Perhaps too little alkalinity (alkalinity can drop fast in our waters if not monitored), or too much calcium. And while I did the AA treatment, and it was successful at removing the colored stains, of what I presumed to be iron colored stains but they always came back. It is possible, please note this is pure conjecture, that the AA removed a veneer of calcium scale, and that iron was not a big a problem as I had always thought. I now believe that was because I never got rid of the underling problem of scale.

    I even believe that I might no longer need to keep my water at a pH of 7.3, but at a more reasonable 7.5 or 7.6, cutting down on acid usage. Only time will tell if that works.

    My present balance is:

    FC 6
    pH 7.3
    TA 80
    CH 375
    CyA 50
    TDS around 880
    Salt around 720
    Temp 78 - 80
    Orthophosphate around 7,500 ppb
    Municipal fill water Orthophosphate around 400 ppb
    Sequestrant 40 ppm

    Thank you to those that help.
    10,000 gal plaster pool,3/4 hp WhisperFlo pump, Sta-Rite Great White GW9500 pool cleaner, Hayward 300 lb Sand Filter
    Use Magenta Stuff for Iron and Silica control.
    Balance: pH 7.7 Cl 7 -8 Alk 70-80 CH 325 CyA 30 in winter - 50 in summer NaCl 1010 TDS 1200

  2. Back To Top    #2

    Join Date
    Mar 2007
    Location
    San Rafael, CA USA
    Posts
    12,082

    Re: What phosphate ppb will precipitate calcium phosphate?

    I thought you already covered this in your hydrogen peroxide to remove metal stains thread where in my post I refer to one of your sources from the previous post that shows the critical calcium hardness and orthophosphate concentrations at different pH.

    This is separate from calcium carbonate scaling. TA affects calcium carbonate scaling which is determined from the saturation index. Calcium phosphate scaling is independent of the TA level (because TA determines the amount of carbonate, for a given pH, but has nothing to do with the level of phosphate).

    According to that link and using it's critical formula:

    pHc = (11.755 - log(CaH) - log(PO4) - 2log(t)) / 0.65
    So solving for phosphate level we have:
    PO4 = 10^[11.755 - log(CaH) - 2log(t) - (0.65 * pH)]
    So for 375 ppm CH, 7.5 pH and 80F (26.67C) we have
    10^[11.755 - log(375) - 2log(26.67) - (0.65 * 7.5)] = 28.44 ppm = 28,440 ppb phosphate

    So your phosphate level would have to get quite high, tough you've had extraordinarily high phosphate in the past due to the amount of metal sequenstrant you have used. Note that the above saturation calculation doesn't necessarily mean scaling occurs just above that level -- it might not occur until some amount of over-saturation, even 2-8 times higher, but it gives you at least some idea.
    16,000 gallon outdoor in-ground 16'x32' plaster pool; Pentair Intelliflo VF pump; Pentair IntelliTouch i9+3s control system; Jandy CL-340 square foot cartridge filter
    12 Fafco solar panels; Purex Triton PowerMax 250 natural gas heater (200,000 BTU/hr output); automatic electric pool safety cover; 4-wheel pressure-side "The Pool Cleaner"

  3. Back To Top    #3

    Join Date
    Aug 2008
    Location
    Honolulu
    Posts
    429

    Re: What phosphate ppb will precipitate calcium phosphate?

    chem geek,

    Thank you for the quick reply.

    Yes I did cover this in the HP post but I never did get the formula right, so once again thank you for writing it out in your post. And yes I do understand that Calcium scaling is not associated with Orthophosphates, I wrote that incorrectly above, thank you for pointing that out.

    I did manage to create an Excel spreadsheet using the formula you wrote out, which must be correct as it agrees with your calculation.

    I will let the pool's pH rise to 7.5 and possibly 7.6 later, and see if any staining returns, if they do I will just have to go back down to 7.3. Obviously I added way too much sequestrant, 40 ppm, but I do not want to drain the pool. I will therefore monitor the orthophosphate levels once every 2 weeks, if it gets within the 28,440 ppb range and staining issues arise it may be necessary to drain some water.

    Two final questions you might be able to help with:

    1. Jack's Magic Sequestrant Test Kit still shows I have around 40 - 42 ppm, which is what I started with. The Orthophosphate level is 7,500 ppb, or 7.5 ppm, should not the sequestrant level have dropped? Or is it possible Jack's Magic adds Orthophosphate to Purple Stuff, I never did test for Orthophosphates when I refilled the pool, after adding the sequestrant? Municipal fill water is only around 400 ppb.

    2. I noticed using your poolequations spreadsheet that raising the pH from 7.3 to 7.5, increases the OCL- would that indicate the oxidizing potential is increased, and does that have any advantages in overall stain control?

    What this has taught me:

    If you remember in the HP post my Orthophosphate levels were very high even before adding a higher amount of sequestrant in the last month or so, much higher than this 28,440 ppb level. I did maintain a maintenance level of 20 ppm, for about a year and a half. I believe that staining issues arose because of the level of Orthophosphate kept increasing by my weekly maintenance of the 20 ppm level, and as I had not drained the pool for sometime.

    To my mind I think that using a sequestrant say at a level of 12 ppm is probably the best solution as it should take a longer time before Orthophosphate levels reach problematic levels. But keeping it at 20 ppm accelerates the need to control this issue. So while higher levels do help to control iron, etc., there is a significant downside. If one also has, as was the case for me, some calcium staining scale as well (before I got rid of them with HP) then the need to monitor these Orthophosphate levels becomes even greater.

    While the calculated threshold level is 28,440 ppb, in the Dow Chemical calculation, probably validated by boiler observations, I agree with you the real number my be much higher. It could also be the case that as swimming pools are so much different from constantly managed water management facilities it might be lower. My own experiment with HP taught me that I needed much more HP, 2.5 times more than water management facilities were using in boilers to remove scale. So we will just have to see what the real world experience ends up being, higher or lower.

    Additionally I now realize that while iron did factor in to staining I think that the greater problem was calcium and phosphate scale that had not been removed and worked as a very efficient sticky trap for metals. And while the AA treatment was very good at removing the top layer of metal staining, the problem of staining always started coming back a few months later because I believe, I could be wrong, I had not treated one major underlying cause, the sticky scale. If the pool stays stain free at the new pH of 7.5-7.6, now that most of the scale has been removed, this would confirm my assumption. If not then I will be wrong, only time will tell.

    Firstly I realize that what I am about to write may not please some people but I think it needs to stated, administrators you are welcome to delete it from this post if you wish. I think there is a small danger in constantly stating Orthophosphate levels do not matter, it is of course true that in regards to algae so long as Chlorine and CyA levels are maintained properly they do not. However if one is constantly using a phosphate based sequestrant such as HEDP then the potential arises for problems, particularly if one is good about adding a weekly dose and does not drain ones pool for many years. Many people never test beyond the 2,500 ppb level, nor know how. A simple Aquarium Phosphate test kit diluted 1:5, 1:10, or 1:20, might give these persons the information they need. I mention Aquarium kits as they are very inexpensive API's kit will do 150 tests. If persons complain of staining it might be a good idea to mention this in replies to them. Asking them if they us a phosphate based sequestrant, how much do they use, and how long have they been using it. If the answers are in the affirmative then having them do a simple test might help. I do realize that the number of people this would apply to would be quite small. But if they do have scale that I now believe needs to be dealt with.

    Finally I note that if I raise the pH from 7.5 to 7.6 then the phosphate threshold drops from 28,440 ppb to 24,492 ppm. If I kept it 7.3 it is 38,373.



    Thank you.
    10,000 gal plaster pool,3/4 hp WhisperFlo pump, Sta-Rite Great White GW9500 pool cleaner, Hayward 300 lb Sand Filter
    Use Magenta Stuff for Iron and Silica control.
    Balance: pH 7.7 Cl 7 -8 Alk 70-80 CH 325 CyA 30 in winter - 50 in summer NaCl 1010 TDS 1200

  4. Back To Top    #4

    Join Date
    Mar 2007
    Location
    San Rafael, CA USA
    Posts
    12,082

    Re: What phosphate ppb will precipitate calcium phosphate?

    Quote Originally Posted by smallpooldad
    1. Jack's Magic Sequestrant Test Kit still shows I have around 40 - 42 ppm, which is what I started with. The Orthophosphate level is 7,500 ppb, or 7.5 ppm, should not the sequestrant level have dropped? Or is it possible Jack's Magic adds Orthophosphate to Purple Stuff, I never did test for Orthophosphates when I refilled the pool, after adding the sequestrant? Municipal fill water is only around 400 ppb.
    I would expect the sequestrant level (if that is measuring HEDP) to drop over time as it gets slowly broken down by chlorine unless you have been adding more sequestrant regularly. I doubt that any of the Jack's Magic products add orthophosphate since there is no good reason to do so for a metal sequestrant.

    Quote Originally Posted by smallpooldad
    2. I noticed using your poolequations spreadsheet that raising the pH from 7.3 to 7.5, increases the OCL- would that indicate the oxidizing potential is increased, and does that have any advantages in overall stain control?
    Raising the pH raises the OCl- hypochlorite ion concentration but lowers the HOCl hypochlorous acid concentration. Both of these are oxidizers and are selective. For some reactions, one participates and the other does not while for other reactions either one participates though perhaps at different rates. Why are you asking about oxidation? For a residential pool with low bather load, the rate of oxidation is generally irrelevant.

    As far as the rate of killing algae or pathogens, that is more dependent on the HOCl level since it is a neutral molecule that looks like water so is able to get past the negatively charged surface of cells more easily than OCl- which is negatively charged. However, with CYA in the water, the HOCl level doesn't change that much with pH while the OCl- changes more vs. pH when CYA is present. But again, why does this matter to you?

    Quote Originally Posted by smallpooldad
    Firstly I realize that what I am about to write may not please some people but I think it needs to stated, administrators you are welcome to delete it from this post if you wish. I think there is a small danger in constantly stating Orthophosphate levels do not matter, it is of course true that in regards to algae so long as Chlorine and CyA levels are maintained properly they do not. However if one is constantly using a phosphate based sequestrant such as HEDP then the potential arises for problems, particularly if one is good about adding a weekly dose and does not drain ones pool for many years. Many people never test beyond the 2,500 ppb level, nor know how. A simple Aquarium Phosphate test kit diluted 1:5, 1:10, or 1:20, might give these persons the information they need. I mention Aquarium kits as they are very inexpensive API's kit will do 150 tests. If persons complain of staining it might be a good idea to mention this in replies to them. Asking them if they us a phosphate based sequestrant, how much do they use, and how long have they been using it. If the answers are in the affirmative then having them do a simple test might help. I do realize that the number of people this would apply to would be quite small. But if they do have scale that I now believe needs to be dealt with.
    I believe you are the only person on this forum with phosphate levels in the multiple tens of thousands and that is due to use of very high levels of HEDP due to the very large amounts of metals being introduced into your pool water on a regular basis. This is not a normal situation so the advice to ignore phosphates is generally sound. It's not absolute in that at some level high phosphates become a problem, not for algae growth (you've proven that chlorine levels alone can prevent that), but with calcium phosphate scaling. The other place where calcium phosphate scale can be an issue is in saltwater chlorine generator cells due to the high pH at the hydrogen gas generation plate, though using 50 ppm Borates cuts down the amount of pH rise in half.

    There is really no advice we give that is absolute in nature. It is all based on usual or typical situations or on factors and parameters that are known. The TA guidelines, for example, assume typical amounts of aeration, but in pools with lots of waterfalls, spillovers, fountains, etc. one may want to target a lower TA than in the recommendations and raise their CH level and target pH level to compensate (i.e. to balance the CSI). Again, there are no absolutes, but we have to generally simplify because it would otherwise be an overload of information for most people who really don't care about the details.

    Nevertheless, for those who are reporting scaling, we can at least ask if they are using a metal sequestrant and if so, what kind and how much. I'll bet, however, that all the reports of scaling are calcium carbonate and not calcium phosphate, except for yours.
    16,000 gallon outdoor in-ground 16'x32' plaster pool; Pentair Intelliflo VF pump; Pentair IntelliTouch i9+3s control system; Jandy CL-340 square foot cartridge filter
    12 Fafco solar panels; Purex Triton PowerMax 250 natural gas heater (200,000 BTU/hr output); automatic electric pool safety cover; 4-wheel pressure-side "The Pool Cleaner"

  5. Back To Top    #5

    Join Date
    Aug 2008
    Location
    Honolulu
    Posts
    429

    Re: What phosphate ppb will precipitate calcium phosphate?

    chem geek,

    Once again thank you for the quick and clear reply.

    Some answers for you:

    1. No I did not add any additional sequestrant since the initial amount of 40 ppm added six weeks ago. Please note that Jack actually recommends 20 ppm for heavy iron issues. If I did not have a sequestrant test kit I might also have followed their instructions by adding a weekly dose, I think 4 to 6 oz I am not sure as I no longer have any bottles. This is something I actually use to do before I got a test kit a year and a half ago. So it is possible to get into trouble fairly quickly, say a year or two if the pool is open 365 days a year, especially if one has an SWG, as I did.

    I have called both Palintest, who supplies Jack's Magic I think, and Jack's Magic to see if the sequestrant test kit also measures Orthophosphate in with the sequestrant, if it does then my sequestrant level would have dropped to around 32.5 ppm of sequestrant. So far no answer yet from either company but I will update when they get back with me (These 2 sentences added as a late edit).

    AS I added 7,100 ppb orthophosphates in 6 weeks with 40 ppm of sequestrant, if the rate continued, I would be at the threshold in 24 weeks, assuming half the dose at 20 ppm, it would take about 48 weeks, if 12 ppm were used it would take about 81 weeks, or about a year and a half. And this is assuming nay another drop for maintenance, which is highly unlikely for pool owners who do not test the sequestrant level. I have also back washed about every 2 weeks in that time. This is assuming the test kit measurement shows no real drop in actual sequestrant, if orthophosphates do affect the test then unless the real level were maintained the weekly additions of orthophosphates would I now realize be lower (This sentence added as a late edit).

    2. I only thought it might matter to our pool in that we have 80% of time fairly strong trade winds which blow a lot of wind borne dirt. I was wondering if a higher OCL- would oxidize some of this more efficiently?

    3. As stated by me I do not think many persons would be affected by phosphate staining, although I think you might lose your bet here on Oahu, and even as stated above on the mainland US, as the "Purple Stuff" is always running out at our local store. Remember we keep our pools operating 365 days a year and many of the pools do operate on the saltwater system, as mine had done for the last 5 years.

    Your point as regards calcium scaling is, I believe, right on the mark as that too is a mineral/iron magnet, in that it too is sticky. I rarely see anyone who recommends the AA treatment ask that question. So perhaps that might be something to ask.

    Thank you for all the help.
    10,000 gal plaster pool,3/4 hp WhisperFlo pump, Sta-Rite Great White GW9500 pool cleaner, Hayward 300 lb Sand Filter
    Use Magenta Stuff for Iron and Silica control.
    Balance: pH 7.7 Cl 7 -8 Alk 70-80 CH 325 CyA 30 in winter - 50 in summer NaCl 1010 TDS 1200

  6. Back To Top    #6

    Join Date
    Aug 2008
    Location
    Honolulu
    Posts
    429

    Re: What phosphate ppb will precipitate calcium phosphate?

    chem geek,

    To use the expression from "Alice in Wonderland", "curiouser and curiouser", something strange has happened to our municipal feed water. I will explain below.

    Jack's Magic tech called me back, within 2 hours he was travelling and on his mobile - great service, he stated he spoke with Jack, Jack thought 20 ppm was about the right amount of "Purple Sequestrant", but not more, for most pools in Hawaii, because of our iron issues. Also after the initial 20 ppm let it go down to between 10 and 12 ppm. But orthophosphate readings and tap water sequestrant concentration (mainly polyphosphates) should be minused out from the pool water sequestrant test.

    I explain the issue of my 42 ppm reading taking out 2 ppm which had always been the tap water level that I had tested in the past, which gave me my original sequestrant level of 6 weeks ago of 40 ppm. Obviously he too was confounded, Jack stated to him not to worry about orthophosphates, but the too should be calculated out of the level

    I tested the tap water again, it may have been two years ago since I tested the tap water. Well guess what the phosphate in the tap water measured around 15 ppm, what the heck happened. I tested twice and yes it is 15 ppm. So the sequestrant level in the pool did drop from 42 (Pool Sequestrant Test) - 15 (Municipal Water Phosphate) - 7.5 (Orthophosphate)= 19.5.

    Then I remembered we received a letter some months back from the Hawaii Board of Water, the State of Hawaii issued a warning to the Hawaii Board of Water for non-testing over a period of some years, but that the levels were not a violation. I looked up the EPA standard for Phosphate in drinking water and in this link it states .015 mg/l, am I correct or incorrect in assuming this is 0.015 ppm? However I also found this article, my question is do I have anything to be concerned about as regards drinking water? Are polyphosphates an issue?

    http://www.phosphatesfacts.org/pdfs/...0Treatment.pdf

    The Orthophosphate test for our fill water only shows 400 ppb, or 0.4 ppm.

    So it seems that part of the orthophosphate level might be attributable to these high other phosphates being introduced to the pool. So you could be, probably are, correct that Jack's stuff may not be the real orthophosphate problem after all but the municipal water may be the issue.

    From reading various articles it seems Polyphosphates break down far more rapidly to Orthophosphate, than does HEDP. This might explain why so many pools in Honolulu, have brown stains. If that is the case, that is something we have to look out for, and of course is a giant pain. Bear in mind with our trade winds and sunny climate water replacement, unless the pool is covered, is at least a bi-weekly or more exercise. Fortunately as explained in the HP post I can reduce large levels of Orthophosphate with HP, typically about 50 to 60 % with each treatment. If no iron staining is present I think I might not need to drop the pH, but have to then add back chlorine, albeit quite a bit of chlorine.

    Jack's tech also told me that their O2 Safe Shock is 12 % dry Hydrogen Peroxide, would the dry HP loose potency as quickly as liquid HP over time?

    You are right it is/was peculiar to my pool, but I think also to other pools in Honolulu, and possibly most of the island of Oahu. That is if the municipal water system use high levels of polyphosphates, it could happen in other parts of the country. Honolulu water infrastructure has been notoriously poorly maintained. In many cases it is over 50 years old; major water main breaks are a near weekly/bi-weekly occurrence, perhaps that is why they are using so much polyphosphate.

    Jack's tech person stated their Phosphate based sequestrants breaks down extremely slowly, and doubts that even at a level of 40 ppm I would have gotten even 1 ppm of Orthophosphate, in a six week period.

    What do you think?

    Thank you.
    10,000 gal plaster pool,3/4 hp WhisperFlo pump, Sta-Rite Great White GW9500 pool cleaner, Hayward 300 lb Sand Filter
    Use Magenta Stuff for Iron and Silica control.
    Balance: pH 7.7 Cl 7 -8 Alk 70-80 CH 325 CyA 30 in winter - 50 in summer NaCl 1010 TDS 1200

  7. Back To Top    #7

    Join Date
    Mar 2007
    Location
    San Rafael, CA USA
    Posts
    12,082

    Re: What phosphate ppb will precipitate calcium phosphate?

    Quote Originally Posted by smallpooldad
    2. I only thought it might matter to our pool in that we have 80% of time fairly strong trade winds which blow a lot of wind borne dirt. I was wondering if a higher OCL- would oxidize some of this more efficiently?
    Dirt is composed of some parts such as rock or other minerals that generally don't get oxidized so have to be filtered out. Soil has some components that get oxidized such as humic and fulvic acids. However, I wouldn't worry about varying the pool pH to handle this as your pool is probably oxidizing these (to the extent it can) fast enough already. If these substances reacted with chlorine but not quickly enough, then they would either 1) show up as Combined Chlorine (CC) or 2) not show up at all and not be a problem either. Substances that don't react with chlorine either dissolve in water or they don't and if they don't then they can be potentially filtered out.

    I would not try and fix problems that do not exist. That is, just because dirt is getting blown into the pool doesn't mean there's a problem to be fixed. If the circulation/filtration is keeping the water clear and you aren't measuring high CC, then you don't have a problem so no need to tinker with the pH or chlorine levels.

    Quote Originally Posted by smallpooldad
    I tested the tap water again, it may have been two years ago since I tested the tap water. Well guess what the phosphate in the tap water measured around 15 ppm, what the heck happened. I tested twice and yes it is 15 ppm.
    :
    I looked up the EPA standard for Phosphate in drinking water and in this link it states .015 mg/l, am I correct or incorrect in assuming this is 0.015 ppm? However I also found this article, my question is do I have anything to be concerned about as regards drinking water? Are polyphosphates an issue?

    http://www.phosphatesfacts.org/pdfs/...0Treatment.pdf

    The Orthophosphate test for our fill water only shows 400 ppb, or 0.4 ppm.
    :
    Jack's tech also told me that their O2 Safe Shock is 12 % dry Hydrogen Peroxide, would the dry stuff loose potency over time?
    I'm confused. You tested your tap water and got 15 ppm (15,000 ppb) phosphates? So what do you mean that the orthophosphate test for your fill water only shows 400 ppb or 0.4 ppm? What was the first test for phosphates -- is that testing for all phosphate including HEDP and polyphosphate?

    My tap water has 300-500 ppb phosphate added to it and it is orthophosphate. As for polyphosphate, it does not break down very quickly from chlorine and it does not degrade quickly. I don't believe it's accurate to say that it breaks down faster than HEDP.

    If your water district is adding 15 ppm polyphosphate, that's a lot, but it probably doesn't get broken down to orthophosphate quickly.
    16,000 gallon outdoor in-ground 16'x32' plaster pool; Pentair Intelliflo VF pump; Pentair IntelliTouch i9+3s control system; Jandy CL-340 square foot cartridge filter
    12 Fafco solar panels; Purex Triton PowerMax 250 natural gas heater (200,000 BTU/hr output); automatic electric pool safety cover; 4-wheel pressure-side "The Pool Cleaner"

  8. Back To Top    #8

    Join Date
    Aug 2008
    Location
    Honolulu
    Posts
    429

    Re: What phosphate ppb will precipitate calcium phosphate?

    chem geek,

    Thank you for the reply did you read my latest post.

    You were right.

    Aloha.
    10,000 gal plaster pool,3/4 hp WhisperFlo pump, Sta-Rite Great White GW9500 pool cleaner, Hayward 300 lb Sand Filter
    Use Magenta Stuff for Iron and Silica control.
    Balance: pH 7.7 Cl 7 -8 Alk 70-80 CH 325 CyA 30 in winter - 50 in summer NaCl 1010 TDS 1200

  9. Back To Top    #9

    Join Date
    Mar 2007
    Location
    San Rafael, CA USA
    Posts
    12,082

    Re: What phosphate ppb will precipitate calcium phosphate?

    See what I just added to my post above regarding your later post (I was still editing my post when you responded above).
    16,000 gallon outdoor in-ground 16'x32' plaster pool; Pentair Intelliflo VF pump; Pentair IntelliTouch i9+3s control system; Jandy CL-340 square foot cartridge filter
    12 Fafco solar panels; Purex Triton PowerMax 250 natural gas heater (200,000 BTU/hr output); automatic electric pool safety cover; 4-wheel pressure-side "The Pool Cleaner"

  10. Back To Top    #10

    Join Date
    Aug 2008
    Location
    Honolulu
    Posts
    429

    Re: What phosphate ppb will precipitate calcium phosphate?

    chem geek,

    I am going to have to make this a quick reply as I am very busy this afternoon and evening.

    If I do a orthophosphate test on tap water with a pool kit, I get around 400 ppm orthophosphates.

    If I do a orthophosphate test on pool water with a pool kit (1:5), and an aquarium test kit 1:5, I get around 7,500 ppm calculated orthophosphates.

    If I do a Jack's Magic (Palintest) sequestrant test kit on tap water I get around 15 ppm, of measured sequestrant.

    If I do a Jack's Magic (Palintest) sequestrant test on pool test I get 42 ppm, of measured sequestrant.

    According to Jack's magic tech person the sequestrant test kit measuring tap water is measuring a sequestrant in all probability Polyphosphates. As I understand it Polyphosphates are much closer to Orthophosphates than HEDP, a Phosphonic Acid, which breaks down more slowly than do Polyphosphates.

    I will call Jack's again tomorrow and see if I can find out more, I will also call the district EPA inspector.

    Thank you for your quick reply and I hope this helps a little.
    10,000 gal plaster pool,3/4 hp WhisperFlo pump, Sta-Rite Great White GW9500 pool cleaner, Hayward 300 lb Sand Filter
    Use Magenta Stuff for Iron and Silica control.
    Balance: pH 7.7 Cl 7 -8 Alk 70-80 CH 325 CyA 30 in winter - 50 in summer NaCl 1010 TDS 1200

  11. Back To Top    #11

    Join Date
    Mar 2007
    Location
    San Rafael, CA USA
    Posts
    12,082

    Re: What phosphate ppb will precipitate calcium phosphate?

    Quoting from the source you linked to on phosphate facts:

    D. Chlorine Stability
    Ortho- and polyphosphates are stable in the presence of chlorine at the levels found in chlorinated potable water. There are no interactions that reduce the levels or effectiveness of either the chlorine or polyphosphate. In addition, iron and manganese sequestered as colorless complexes before chlorination will remain colorless after chlorination.
    Now, polyphosphates come in all different types, but I presume they mean inorganic polyphosphates. Some are cyclical, such as sodium hexametaphosphate, while others are linear. They are orthosphophate linked by oxygen in an ester chain.

    Where are you getting your information that polyphosphates get oxidized by chlorine and that they do so faster than HEDP? When we recommend HEDP over other metal sequestrants, it's not so much over other polyphosphates, but over other metal sequestrants such as EDTA that does break down from chlorine more quickly.
    16,000 gallon outdoor in-ground 16'x32' plaster pool; Pentair Intelliflo VF pump; Pentair IntelliTouch i9+3s control system; Jandy CL-340 square foot cartridge filter
    12 Fafco solar panels; Purex Triton PowerMax 250 natural gas heater (200,000 BTU/hr output); automatic electric pool safety cover; 4-wheel pressure-side "The Pool Cleaner"

  12. Back To Top    #12

    Join Date
    Aug 2008
    Location
    Honolulu
    Posts
    429

    Re: What phosphate ppb will precipitate calcium phosphate?

    chem geek,

    I apologize if I gave the impression that HEDP gets reduced to orthophosphates quickly, what I meant to write is that some forms of Polyphosphates can be reduced more quickly, EDTA may be such an example, but not being a chemist I cannot verify this. I am aware that HEDP breaks down very slowly thanks to Jack's tech person.

    Jack's tech person asked me to email Jack personally to ascertain what might be going on. This I did this morning, below is a copy of that email. I will get back to you when a reply is received.

    I will wait on calling the EPA until I know what if any are the issues, although it has been reported in the local news, on a number of occasions, that the Board of Water has been very short of personnel.

    Additionally the pH is now 7.5 and not 7.3, no stains are showing their ugly head, thank goodness.

    Thank you.

    Jack,

    Barry asked me to email you these questions. When testing tap water I get a reading of 15 ppm, 2 years ago it read 2 ppm, what is it that the your sequestrant test kit is reading? Is it phosphates, and if so what type of phosphates might they be, or is it another mineral, or chemicals and if so what might they be?

    When I measure the pool with your sequestrant test kit I get a reading of 42 ppm, if I use an aquarium orthophosphate test kit I get 7.5 ppm for pool water. Barry stated that I should deduct the 15 from the 42 which would give me 27 ppm. But he stated not to deduct the pool orthophosphate reading of the pool, which is 7.5 ppm. I realize that 2 bottles was too much to have added.

    The tap water (fill water) orthophosphates read 400 ppb (0.4 ppm), with a pool orthophosphate test.

    To give you a little history, I drained the 10,000 gallon pool about 6 weeks ago and added 2 x 32 oz bottles off the "Purple Stuff". At the time I did not test the tap water with your kit, but I did test the pool water and it came in at 42 ppm. The "Blue Stuff" is not available in our area.

    Prior to draining the pool which was saltwater at the time, I treated it over night with about 28 bottles of 3% Hydrogen Peroxide and 1 lb of Ascorbic Acid, to remove calcium, iron, and phosphate scale. Before sunrise the pool was completely drained. The staining was not heavy but after the drain there was quite a bit of white and light yellow-brown sand/powder at the bottom of the pool, it looked like a mini beach. I refilled and backwashed 3 times in a 48 hour period which seems to have removed this sand/powder.

    The balance of the pool which is no longer saltwater but maintained with an 8% bleach solution was as follows:

    FC 6
    pH 7.3 (now 7.5)
    TA 80
    CH 375
    CyA 50
    TDS around 880
    Salt around 720
    Temp 78 - 80
    Orthophosphate around 7,500 ppb
    Municipal fill water Orthophosphate around 400 ppb
    Sequestrant 42 ppm - 15 ppm (from fill water test) = 27 ppm

    Might you have any idea why the orthophosphate level reached 7.5 ppm in such a short period of time - 6 weeks, could it be the type of phosphates the Hawaii Board of Water of water supply is adding, if they are (poly) or other phosphates do they breakdown this rapidly into orthophosphates, in chlorine, and in the strong UV light we have in Honolulu? Could they be using EDTA?

    Additional information is that we received a letter some months back from the Hawaii Board of Water, the State of Hawaii issued a warning to the Hawaii Board of Water for non-testing over a period of some years, but that the levels were not a violation, although nitrates might have been too high.

    Honolulu water infrastructure has been notoriously poorly maintained. In many cases it is over 50 years old; major water main breaks are a near weekly/bi-weekly occurrence, perhaps that is why they are using so much (poly) or other phosphate.

    I looked up the EPA standard for Phosphate in drinking water and it stated .015 mg/l, am I correct or incorrect in assuming this is 0.015 ppm? Do the above numbers appear to be a violation?

    Currently I raised the pH to 7.5 without seeing any stains re-appear, Hawaii does have iron issues, because of the brown dirt (ferric oxide) blown into our pools by trade winds that average year round at between 20 and 28 mph on our hill. Brown stained pools are a common site in residential areas.

    I also 2 days ago added 2/3 of a bottle of your "Magenta Stuff". All readings shown here were taken prior to this addition.

    Final question if I purchased your O2 shock, which I understand to be 12% dry Hydrogen Peroxide, for each 1 lb put into a 10,000 gallon pool (assuming chlorine reads zero) what would be the ppm of HP in the pool.

    Finally I have used your products for many years now and have been extremely happy with the results, also the service I receive from your help number is excellent. Barry returned my call very promptly; and although I called him back on his mobile at nighttime he was very courteous and helpful. You really run a great company and I think we pool owners all thank you for that.

    Looking forward to your reply. If you have any further questions please email me.

    Aloha,
    10,000 gal plaster pool,3/4 hp WhisperFlo pump, Sta-Rite Great White GW9500 pool cleaner, Hayward 300 lb Sand Filter
    Use Magenta Stuff for Iron and Silica control.
    Balance: pH 7.7 Cl 7 -8 Alk 70-80 CH 325 CyA 30 in winter - 50 in summer NaCl 1010 TDS 1200

  13. Back To Top    #13

    Join Date
    Mar 2007
    Location
    San Rafael, CA USA
    Posts
    12,082

    Re: What phosphate ppb will precipitate calcium phosphate?

    Quote Originally Posted by smallpooldad
    I apologize if I gave the impression that HEDP gets reduced to orthophosphates quickly, what I meant to write is that some forms of Polyphosphates can be reduced more quickly, EDTA may be such an example, but not being a chemist I cannot verify this. I am aware that HEDP breaks down very slowly thanks to Jack's tech person.
    The only forms of polyphosphates that would be expected to break down more quickly would be those with groups that chlorine attacks such as the amine group in the organic polyphosphate Adenosine diphosphate (ADP). EDTA is not a polyphosphate and contains no phosphate.
    16,000 gallon outdoor in-ground 16'x32' plaster pool; Pentair Intelliflo VF pump; Pentair IntelliTouch i9+3s control system; Jandy CL-340 square foot cartridge filter
    12 Fafco solar panels; Purex Triton PowerMax 250 natural gas heater (200,000 BTU/hr output); automatic electric pool safety cover; 4-wheel pressure-side "The Pool Cleaner"

  14. Back To Top    #14

    Join Date
    Aug 2008
    Location
    Honolulu
    Posts
    429

    Re: What phosphate ppb will precipitate calcium phosphate?

    chem geek.

    Thank you for your reply and clarification.

    No response from Jack yet, or Palintest, but it does now seem from what I have been reading today that the Board of Water can introduce legally other phosphates mixes into the water supply. Depending on the phosphate type, the percentage can legally go as high as 36.0 mg/l, I think this is 36 ppm. In fact it seems that the Board of Water maybe doing the right thing to help the water system in Honolulu by adding these sequestrant/phosphate blend, maybe they got a better chemist.

    I will try and call them tomorrow, although they are very hard to get a hold off, also they may not wish to divulge what they are using.

    Concerning the calculation, Jack's tech tells me not to subtract orthophosphates from the results, but everywhere else I read that one should deduct them from the test. Maybe Jack will clarify this.

    I also found some other information that might throw a light on why the orthophosphates are multiplying so rapidly but I will wait until till I talk with the chemist at the Board of Water before I go over those findings.

    The response back to you may take a few days. The pool is looking good but I did lower the pH from 7.5 to 7.4, I will cover why in my response.

    Have a pleasant weekend if I do not get back with you sooner.
    10,000 gal plaster pool,3/4 hp WhisperFlo pump, Sta-Rite Great White GW9500 pool cleaner, Hayward 300 lb Sand Filter
    Use Magenta Stuff for Iron and Silica control.
    Balance: pH 7.7 Cl 7 -8 Alk 70-80 CH 325 CyA 30 in winter - 50 in summer NaCl 1010 TDS 1200

  15. Back To Top    #15

    Join Date
    Aug 2008
    Location
    Honolulu
    Posts
    429

    Re: What phosphate ppb will precipitate calcium phosphate?

    chem geek,

    No news from Jack, or Palintest.

    Board of Water chemist did call me back about 2 hours after I called, so pleasantly surprised by the quick response. He stated they do use a small amount of Sodium Hypochlorite to sanitize water, but they do NOT use any sequestrant/phosphates. He asked me what test I was using, I explained it was the Thorium Nitrate test, he too agreed that that is an accurate test. He asked me to bring in a sample next week. I asked how many days would it take to get results but he could not tell me when the analysis will be available.

    The only thing I can think of is that maybe somewhere along the line from the 5 pumping stations supplying our area that agricultural phosphate is seeping into the line, but that really would be odd.

    I note that the test can be affected by iron, orthophosphate, polyphosphate, chelants, and fluoride. Fluoride is not added to our water, and to the best of my knowledge the amount of iron is negligible, as is the orthophosphate level.

    I re-tested the pool for orthophosphate, and the level has risen from 7,500 to 10,000 ppb in a week, very odd. Only thing I can think of is that maybe fertilizer dust is blowing in with strong tradewinds from the agricultural farms behind our mountain; this really is a mystery.

    Obviously I need to keep a real close eye on orthophosphate levels, if this keeps up. If they do keep increasing I will be stuck with whacking them back down with HP every so often.

    I also tested nitrates, but nothing really interesting there, about 2 ppm from the tap water, about 4.5 ppm in the pool.

    It might be a while before I get back with you.

    Have a nice weekend.
    10,000 gal plaster pool,3/4 hp WhisperFlo pump, Sta-Rite Great White GW9500 pool cleaner, Hayward 300 lb Sand Filter
    Use Magenta Stuff for Iron and Silica control.
    Balance: pH 7.7 Cl 7 -8 Alk 70-80 CH 325 CyA 30 in winter - 50 in summer NaCl 1010 TDS 1200

  16. Back To Top    #16

    Join Date
    Aug 2008
    Location
    Honolulu
    Posts
    429

    Re: What phosphate ppb will precipitate calcium phosphate?

    chem geek,

    One other strange thing, the CyA keeps dropping. Last weekend it went from 50 some two weeks before to 40, last Sunday I added back to bring it back to 50, by Wednesday it was 50, but this morning it is 45. In other words it seems to be dropping too fast. I do the test the same way each time, so it is definitely dropping. I realize the actual real number may be different.

    Looking through your posts I found this:

    http://www.troublefreepool.com/degra...cya-t8880.html

    It mentions "Nitrosomonas", cross referencing this on the net, it seems to convert Polyphosphate to Orthophospates at a fairly rapid rate albeit at a higher pH, this might be why I am encountering the fairly rapid growth of Orthophosphates. The articles say to shock at a level of between 5 and 10 ppm for water treatment facilities but the pH is generally speaking higher than my 7.4.

    Also in 6 weeks nitrates grew from 2 ppm to 4.5 ppm, I do not think that is significant, or is it?

    We did have some very strong winds blowing over the islands in the last two weeks, the remains of one hurricane, and one tropical depression passing to the south of the island chain. Our pool tables and chairs have a fairly thick layer of dirt on them. "Nitrosomonas" can be introduced by debris as I understand it. The pool however still looks great, no staining, no CC, chlorine demand is up a little but not by much.

    I plan on shocking the pool to the 50 ppm of CyA level overnight to see if that might help. The level I will raise it to is 19.8 ppm of Chlorine, unless you think I should go with Yel/MstrdShock level of 29.42, or perhaps not do it at all. We are 3 hours behind the West Coast, and 6 hours behind the East Coast. I plan on doing this overnight from around 7 pm this evening. If you can let me know what you think that would be great. If I do not hear from you this is what I will do, unless you think it is a waste of time.

    I will add the necessary acid to compensate for the rise in pH incurred by the Chlorine.

    Thank you for your time.
    10,000 gal plaster pool,3/4 hp WhisperFlo pump, Sta-Rite Great White GW9500 pool cleaner, Hayward 300 lb Sand Filter
    Use Magenta Stuff for Iron and Silica control.
    Balance: pH 7.7 Cl 7 -8 Alk 70-80 CH 325 CyA 30 in winter - 50 in summer NaCl 1010 TDS 1200

  17. Back To Top    #17

    Join Date
    Mar 2007
    Location
    San Rafael, CA USA
    Posts
    12,082

    Re: What phosphate ppb will precipitate calcium phosphate?

    So long as you have at least some chlorine in the pool, you don't have living bacteria that could cause the degradation (assuming you don't have already established biofilms, but those won't form if you always kept chlorine in the pool at proper levels). Any bacteria getting blown in would get killed before they are even able to reproduce in one generation. If you have a sand filter, you could check it to see if you have biofilms in it causing clumps and channeling, but usually that's only seen in high bather-load commercial/public pools.

    CYA does get oxidized by chlorine, but fairly slowly. Some people report up to 10 ppm CYA per month loss, though for most it's less and in hot residential spas we see around 5 ppm CYA per month loss. In my pool it's low at around 2-3 ppm CYA per month loss, but I have a mostly opaque electric safety cover on most of the time (except for 1-2 hours per day pool use). It's possible for the hydroxyl radicals created when chlorine breaks down from the UV in sunlight accelerate the oxidation of CYA, but it's not as fast a drop as you are seeing. Then again, I wouldn't take a single reading as meaning anything given the variability in the test itself -- see if there is a trend over time.

    You've got a whole bunch of mysteries in your pool. You are measuring lots of polyphosphates, but the water supply company says they aren't adding any. You are having a faster CYA loss and a rise in orthophosphates. Are you sure you aren't getting water dilution? Don't you get rains during the day where you live and doesn't the water overflow the pool as a result?

    We know that the HEDP will break down to increase the orthophosphate level and though that is somewhat slow, your HEDP level is high so even at 10% degradation per week, 10,000 ppb (10 ppm) HEDP would result in 10%*15,000*2*94.9714/206.028 = 922 ppb orthophosphate per week. So I don't think that your having more orthophosphates over time is much of a mystery. Again, it is well known that chlorine slowly oxidizes HEDP to break it down to orthophosphate though the rate may not be as high as the 10% per week I used in the example, but remember that if it wasn't getting oxidized then you wouldn't need to keep adding more to your pool (except to make up for water dilution). This oxidation does not occur with ordinary polyphosphate (phosphates in an ester chain).
    16,000 gallon outdoor in-ground 16'x32' plaster pool; Pentair Intelliflo VF pump; Pentair IntelliTouch i9+3s control system; Jandy CL-340 square foot cartridge filter
    12 Fafco solar panels; Purex Triton PowerMax 250 natural gas heater (200,000 BTU/hr output); automatic electric pool safety cover; 4-wheel pressure-side "The Pool Cleaner"

  18. Back To Top    #18

    Join Date
    Aug 2008
    Location
    Honolulu
    Posts
    429

    Re: What phosphate ppb will precipitate calcium phosphate?

    chem geek,

    Thank you for incredibly fast reply it is much appreciated.

    I just got back from my older grandson's birthday party, too many kids in their pool. And my young grandson's soccer match, he is only six and the shortest guy on the team but fearless and very tough, he scored 2 goals, and they won 4 to 2.

    So your news that I will not have to shock the pool comes as a pleasant surprise, to end a surprisingly pleasant day.

    We do get rains but the evaporation is so high, mainly due to wind and on very sunny days heat, that they balance each other out, in fact I have to add water, and some 10 to 20 ppm of alkalinity if the rains have been heavy. On a few occasions a year the rain might stall over Hawaii for a week or 10 days and then yes draining might be required, but it has been many months since that happened.

    I will just have to wait on the Board of Water's answer. There exists the possibility that my sequestrant test solution and tablets, could be older than marked, and this might skew the results. Although the Orthophospates are tested with 2 separate brand new kits.

    The detailed explanation you gave, particularly to the rates of possible breakdown of both CyA and HEDP to orthophosphate, puts my mind at peace. Once I get results back from the Board of Water I may just drain down some, once I know what the real level of Polyphosphates are, to remove excessive sequestrant, and treat the pool with some HP to get the orthophosphates to a lower level.

    The pool really does look great right now, and this is the first time in many years, possibly 10 years, that iron type staining has not started to raise it's ugly head starting as always first on the steps. This normally occurred after 4 to 6 weeks very, very faintly at first but then started to build over most horizontal surfaces, then at 6 to 9 months it became too noticeable an AA treatment was therefore necessary.

    To this I do attribute the 2.5 times HP (Hydrogen Peroxide) treatment done in combination with 1 lb of AA (Ascorbic Acid) which removed a lot of both calcium and iron/phosphate scale. The complete drain of course helped take out what remaining iron may still have been in solution. I realize that this may not be a solution for everyone but with a relatively small pool of 10,000 or 15,000 gallons it seems to me if one can drain it is a good idea, although the results might not have been too different had I not drained.

    I will keep you up-to-date when I get the report back.

    And once again, thank you for saving me time and money.
    10,000 gal plaster pool,3/4 hp WhisperFlo pump, Sta-Rite Great White GW9500 pool cleaner, Hayward 300 lb Sand Filter
    Use Magenta Stuff for Iron and Silica control.
    Balance: pH 7.7 Cl 7 -8 Alk 70-80 CH 325 CyA 30 in winter - 50 in summer NaCl 1010 TDS 1200

  19. Back To Top    #19
    Patrick_B's Avatar
    Join Date
    Jun 2011
    Location
    Midland TX
    Posts
    15,001

    Re: What phosphate ppb will precipitate calcium phosphate?

    I thought I was interested in, and liked fooling around with Pool Chemistry. Apparently not as much some.
    TFP Moderator
    Essential Links:
    ABC's Of Pool Chemistry, Test Kits, SLAM Your Pool
    28K Gal IG FreeForm, CLI Quartz, Pentair 36"SF & VS Pump, Dolphin M5, Rheem

  20. Back To Top    #20
    Swampwoman's Avatar
    Join Date
    Apr 2012
    Location
    Grand Rapids, MI
    Posts
    3,533

    Re: What phosphate ppb will precipitate calcium phosphate?

    I know this is a long-dead thread but today I've had an experience that corroborates Smallpooldad's experience and wanted to post it for posterity.

    I changed my heavy-phosphate-level water mid-August during a liner change.
    I had city water trucked in.
    I continued using Jacks Purple for SWG, because I was still getting lw level iron staining, that as it turns out, may have been coming from an old, coroding ladder subsequent to swg switch. I don't ave the sequestrant test kit, so have used the recommended maintenance dose on the bottle.

    10 weeks later, I read the po4 level with my hi limit Hanna tester: 11,400 ppb aka 11.4 ppm. In other words, about 1,000 ppb a week since clean start after start up dose.

    Right now, I am keeping water super hot for imminent installation of a dome next week, and with leaf traffic, can't do a phosphate removal floc at the moment. But running a heater hot will likely mean that I will soon have to do so to avoid the kind of phosphate scaling I was getting prior to the water change.

    At this point, based on my experience to date, I personally believe the rate of HEDP breakdown is substantially faster than any of the mfg techs would have one believe.

    Smallpooldad and I were using the same product and experiencing the same rate of po4 accumulation in terms of ppb per week. He is in Hawaii and I am in Michigan.

    Since I am currently not seeing scale shedding from returns, I will begin weekly po4 reduction treatments to get through the winter without doubling or tripling my po4, since in my case the scaling seems to occur in the 25,000+ range. I will then do an alum floc come spring.
    In ground extended Grecian, 22,000 gal, Hayward 220t sand filter, vinyl liner, dolphin m4 supreme.
    If TFP has helped you, please click to SUPPORT TFP!
    Helpful Links:
    GET A TEST KIT Chlorine/CYA Chart How to SLAM About Metals & Stains

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •