Will Phosphates increase chlorine demand?

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benavidescj

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Apr 27, 2010
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I can say with certainty that the combination of Suncoast All In One Algaecide and Suncoast Chemicals Salinity Stain Control has at least some effect on the SWG's ability to produce chlorine. I continue to lose 3 -4 ppm chlorine per day. My next step is to add the phosphate remover and see if the loss continues. However, I did this before and chlorine levels began to hold.
 

chem geek

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We know that some algaecides, such as Polyquat, most certainly increase chlorine demand if you use a lot of it because chlorine breaks them down (it's not much in maintenance doses, but for high initial doses it's usually noticeable). We also know that stain removers also increase chlorine demand for the same reason, though EDTA-based ones break down much faster than HEDP. If you stop adding such products, then they will continue to break down and lower in concentration and the chlorine demand will drop. You should try that first; otherwise, you'll attribute the drop to the phosphate remover inappropriately.

I don't know why you didn't use 0-20-0 fertilizer I suggested for doing your experiment since that contains only orthophosphate. You'd need to add enough to overcome the phosphate remover you've already added. By using these other algaecide and metal sequestrant products you are mixing up chlorine demand from their breakdown along with release of orthophosphate (from HEDP). That's no way to do an experiment -- mixing multiple variables together both having affect on chlorine demand. Quite frankly, if you don't explicitly do the experiment using orthophosphate directly, then I consider your results invalid as far as concluding something specifically attributed to phosphates alone.
 

UnderWaterVanya

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While I agree with chem geek that the best experiment is the simple one - if the phosphate remover isn't used and the chlorine demand eases up and the SWGC still isn't producing - that could be a sign of potential for further experimentation.
 

benavidescj

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chem geek said:
We know that some algaecides, such as Polyquat, most certainly increase chlorine demand if you use a lot of it because chlorine breaks them down (it's not much in maintenance doses, but for high initial doses it's usually noticeable). We also know that stain removers also increase chlorine demand for the same reason, though EDTA-based ones break down much faster than HEDP. If you stop adding such products, then they will continue to break down and lower in concentration and the chlorine demand will drop. You should try that first; otherwise, you'll attribute the drop to the phosphate remover inappropriately.

I don't know why you didn't use 0-20-0 fertilizer I suggested for doing your experiment since that contains only orthophosphate. You'd need to add enough to overcome the phosphate remover you've already added. By using these other algaecide and metal sequestrant products you are mixing up chlorine demand from their breakdown along with release of orthophosphate (from HEDP). That's no way to do an experiment -- mixing multiple variables together both having affect on chlorine demand. Quite frankly, if you don't explicitly do the experiment using orthophosphate directly, then I consider your results invalid as far as concluding something specifically attributed to phosphates alone.
Chem geek, I don't appreciate how you approached your response. Apparently you think I am a chemist and have somehow disgraced the profession. I am not a chemist.

I did not use the 0-20-0 to spite you, I simply wanted to recreate the previous results using the EXACT same chemicals I used before. Now that I have and know which chemicals are causing the issue I can do further testing.

However, If you would have read my previous posts closer, you would see where I stated that adding the metal sequestrant alone had NO effect on chlorine demand. Only in the presence of poly. If I now remove the phosphate from the water and as I expect the chlorine demand to drop significantly, I have a result. The result is that somehow the metal sequestrant and the poly interact somehow to increase chlorine demand. I am not referring to increase in chlorine demand of each product in isolation, it is an interaction that is increasing the demand.
 

chem geek

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The assertion was that phosphates stop the SWCG from outputting chlorine. That assertion should be proved or disproved first. What you are now describing is a possible interaction between Polyquat and metal sequestrant that increases chlorine demand (and maybe leads to a breakdown of HEDP to produce orthophosphate). That's a different issue to be looked at. It's fine to look at each separately, but the topic of this thread started out and is mostly about phosphates preventing an SWCG from producing enough chlorine and that adding a phosphate remover fixed that problem. The best way to do that experiment is by explicitly adding phosphates to the water (such as with phosphate-only fertilizer) to reproduce the problem and then use a phosphate remover to fix the problem, then repeat just to be sure (making sure to add enough phosphates to overcome any residual phosphate remover).
 

benavidescj

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chem geek said:
The assertion was that phosphates stop the SWCG from outputting chlorine. That assertion should be proved or disproved first. What you are now describing is a possible interaction between Polyquat and metal sequestrant that increases chlorine demand (and maybe leads to a breakdown of HEDP to produce orthophosphate). That's a different issue to be looked at. It's fine to look at each separately, but the topic of this thread started out and is mostly about phosphates preventing an SWCG from producing enough chlorine and that adding a phosphate remover fixed that problem. The best way to do that experiment is by explicitly adding phosphates to the water (such as with phosphate-only fertilizer) to reproduce the problem and then use a phosphate remover to fix the problem, then repeat just to be sure (making sure to add enough phosphates to overcome any residual phosphate remover).
I never made an assertion. I simply asked a question based on initial observations to others that may have more knowledge than myself. After 3 pages of interaction with you and other members as well as some initial testing on my part it is apparent that phosphates alone do not have an appreciable effect on chlorine demand. This is true at least at the levels around 2000ppb. I could split this thread off and the moderator may want to but the history that got us to this point may get lost. The title still has relevance since it appears that phosphate does have an indirect effect here.

Adding phosphates alone at this point using 0-20-0 is, well, pointless since I already know that phosphates do not increase chlorine demand. I have a measurable amount of phosphates in the water that was added using the metal sequestrant. The point at which the chlorine demand went up was when I added the poly in the presence of the metal sequestrant. The other observation that I still have to reproduce is the loss of chlorine demand when phosphate remover is added. I plan on doing that this evening after taking one more final chlorine level reading.
 

chem geek

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Until the metal sequestrant breaks down by oxidation from chlorine (and possibly by some new interaction you are seeing with Polyquat), it isn't counted as phosphate -- it's not orthophosphate. The metal sequestrant HEDP is an organic phosphate and is not rapid food for algae and is very unlikely to have any effect on an SWCG and is also not removed by a phosphate remover. That's why I don't consider that part of the experiment valid in terms of attributing anything to "phosphate" or to a phosphate remover.

You showed how a phosphate remover made the SWCG be able to either produce more output or for its output to last longer (i.e. not get consumed as quickly in the bulk pool water). What we don't know is whether this effect is due to a more direct effect associated with the orthophosphate level. We know that phosphates are an essential nutrient for algae growth so if the FC/CYA ratio isn't high enough then nascent algae growth can outrun the ability of an SWCG to produce enough chlorine. What we don't know is whether there is another more direct effect of phosphates on SWCG chlorine production such as some sort of scaling (calcium phosphate or other phosphate scale). If the maintained FC level were high relative to CYA (even if maintained manually during the experiment), then we could focus on this direct phosphate effect on the SWCG by seeing if the SWCG was able to output and maintain chlorine at high phosphate levels.

Separate from the above we have the Polyquat and HEDP interaction. Here too we don't know whether the issue is solely one of some sort of catalytic or other chemical reaction that consumes chlorine (which we know does break down both chemicals, but perhaps their combination accelerates such breakdown) or whether it is just HEDP breaking down more quickly in the presence of Polyquat thereby releasing orthophosphate with whatever effects orthophosphate has on its own.
 

benavidescj

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chem geek said:
Until the metal sequestrant breaks down by oxidation from chlorine (and possibly by some new interaction you are seeing with Polyquat), it isn't counted as phosphate -- it's not orthophosphate. The metal sequestrant HEDP is an organic phosphate and is not rapid food for algae and is very unlikely to have any effect on an SWCG and is also not removed by a phosphate remover. That's why I don't consider that part of the experiment valid in terms of attributing anything to "phosphate" or to a phosphate remover.
I tried to find out what exactly the Taylor K-1106 phosphate test is testing for but all it says is "phosphate". This is the test kit I am using. The previous time when the phosphate level was high, be it orthophosphate or some other variant the phosphate remover lowered the level as tested by the K-1106. The reading went from approx 1500ppb down to below 125ppb (the lowest reading for this kit).

chem geek said:
You showed how a phosphate remover made the SWCG be able to either produce more output or for its output to last longer (i.e. not get consumed as quickly in the bulk pool water). What we don't know is whether this effect is due to a more direct effect associated with the orthophosphate level. We know that phosphates are an essential nutrient for algae growth so if the FC/CYA ratio isn't high enough then nascent algae growth can outrun the ability of an SWCG to produce enough chlorine. What we don't know is whether there is another more direct effect of phosphates on SWCG chlorine production such as some sort of scaling (calcium phosphate or other phosphate scale). If the maintained FC level were high relative to CYA (even if maintained manually during the experiment), then we could focus on this direct phosphate effect on the SWCG by seeing if the SWCG was able to output and maintain chlorine at high phosphate levels.
I was careful this time, even though I think I was last time, to ensure that the chlorine level was high for my CYA of 70 so I don't think algae is a player here. This conclusion is solidified by the fact that I continue to pass overnight FC testing. I believe I have already shown that there is no direct effect of phosphate on the SWCG, unless you are referring to orthophosphate, as I added the metal sequestrant in isolation prior to adding the poly.

chem geek said:
Separate from the above we have the Polyquat and HEDP interaction. Here too we don't know whether the issue is solely one of some sort of catalytic or other chemical reaction that consumes chlorine (which we know does break down both chemicals, but perhaps their combination accelerates such breakdown) or whether it is just HEDP breaking down more quickly in the presence of Polyquat thereby releasing orthophosphate with whatever effects orthophosphate has on its own.
This line of thinking is of more interest to me. I believe there is some sort of interaction. What I don't know, and you may, is the time required to complete the breakdown. I have been at this for over a week and a half. I see no real decline in chlorine demand. Is this not sufficient time to breakdown these compounds?

Finally, I think you would like to see me add the 0-20-0 then poly for a future round of testing?
 

JasonLion

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Polyquat can continue interacting with chlorine for some time.

The obvious next step to separate the effects of phosphates from the effect of polyquat. So far all you have conclusively demonstrated is extra chlorine demand from polyquat, which is expected. There are some hints that there might be some additional interaction present, but nothing conclusive.

There are several ways to proceed to narrow things down. One approach would be to add the same amount of polyquat while phosphates are very low. To do that will require both eliminating the phosphates and eliminating the current chlorine demand first. If chlorine demand is the same in that situation then we know it is simply polyquat, while if chlorine demand is lower, then we know there is some interaction between phosphates and polyquat.

Another line of investigation is to check to see if phosphate remover again stops the chlorine demand. The result of that test alone doesn't prove anything however, we then need to see if phosphate remover is interacting with the polyquat directly or if phosphates are required for the change in chlorine demand to occur. Phosphate remover includes clarifier, which might well be binding directly to the polyquat and removing it, separately from anything to do with phosphates.
 

benavidescj

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JasonLion said:
There are several ways to proceed to narrow things down. One approach would be to add the same amount of polyquat while phosphates are very low. To do that will require both eliminating the phosphates and eliminating the current chlorine demand first. If chlorine demand is the same in that situation then we know it is simply polyquat, while if chlorine demand is lower, then we know there is some interaction between phosphates and polyquat.
Jason, one thing to recall is that chlorine demand only went away when phosphate remover was used in the presence of poly. This means one of two things. Either the phosphates were the issue or the interaction with poly. Since I added phosphates, even though it was with metal sequestrant which may be an issue, it was present prior to poly and had no effect on chlorine demand.

JasonLion said:
Another line of investigation is to check to see if phosphate remover again stops the chlorine demand. The result of that test alone doesn't prove anything however, we then need to see if phosphate remover is interacting with the polyquat directly or if phosphates are required for the change in chlorine demand to occur. Phosphate remover includes clarifier, which might well be binding directly to the polyquat and removing it, separately from anything to do with phosphates.
I like your thinking here. knowing what it is about the phosphate remover that is reversing the chlorine demand may prove challenging.
 

chem geek

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benavidescj said:
I tried to find out what exactly the Taylor K-1106 phosphate test is testing for but all it says is "phosphate". This is the test kit I am using. The previous time when the phosphate level was high, be it orthophosphate or some other variant the phosphate remover lowered the level as tested by the K-1106. The reading went from approx 1500ppb down to below 125ppb (the lowest reading for this kit).
That kit tests for orthophosphate only and uses the "stannous chloride" method. It is not a test for organic phosphate such as HEDP nor for polyphosphate. The method is described in this post though in the context of measuring phosphate in blood serum. Now over time chlorine will break down HEDP to orthophosphate, but normally this doesn't happen very quickly. If you measure phosphate increasing significantly after adding HEDP, then something is breaking it down more quickly.

benavidescj said:
Finally, I think you would like to see me add the 0-20-0 then poly for a future round of testing?
Well, based on what you saw that only having Polyquat in the mix was causing you excessive chlorine demand, then this phosphate-only experiment isn't necessary unless someone believes that phosphates alone cause SWG cells to either not output chlorine or to increase chlorine demand (other than by algae growth) so that the SWG cannot keep up.
 

benavidescj

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Well, I never did add the phosphate remover. The chlorine demand (or lack of chlorine production by the SWCG) seems to have gone down on it's own. So now I am thinking that the Poly is what was causing the issue all along. I also think that the loss of chlorine demand with the addition of phosphate remover before was just a coincidence. It seems to take some time (>10 days) for chlorine to break Poly down. I am still scratching my head on why the overnight testing was always negative. If there is chlorine demand during the day there should be chlorine demand at night. Or is it that the Poly was just blocking the ability of the SWCG to produce chlorine?? The later seems more logical to me.

Here again is proof that phosphates do not have an affect on chlorine demand at least at lower concentrations. I still have 2000ppb with no demand. I wish the SWCG OEMs would stop looking at this as an issue. Or is it that they need yet another reason not to comply with warranty claims.
 

chem geek

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Thanks for the research. Polyquat usually breaks down about half each week at usual pool FC/CYA levels which is why it is added in weekly maintenance doses. I wrote this thread at The PoolForum about the chlorine oxidation of Polyquat and figured out that roughly every 5 fluid ounces of 60% Polyquat has a chlorine demand of 1 ppm FC per 10,000 gallons. The recommended maintenance dose is 3 ounces per 10,000 gallons so the chlorine demand is pretty small. If you do a larger "visible algae growth" dose of 16 ounces per 10,000 gallons, then that's a chlorine demand of 3.2 ppm FC which is more noticeable, though still not huge since it's over a week's time. This would come to only 0.02 ppm FC per hour so overnight would probably not be that noticeable at around 0.24 ppm FC over 12 hours.

It's possible that the Polyquat breaks down faster during the day to due to the breakdown of chlorine from sunlight that produces hydroxyl radicals, but that wouldn't increase chlorine demand. Maybe there is some more direct interference of Polyquat with the salt cells, though I don't know what they would be.

We know that linear quats break down faster with chlorine so their apparent chlorine demand is higher, assuming one keeps replenishing the algaecide.
 

swimcmp

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Well very interesting but we are in the midwest and have about 60-70 customers with swcg's. We don't sell polyquat to our customers. Don't believe in selling what they don't need. Strange huh? But I have seen customers with phosphates in the 3,5-5000 range and unable to establish a chlorine reading. Lower the phosphates and they then can maintain chlorine. Less is better imo, if you have to buy chlorine to maintain a swcg pool why have a swcg, defeats the purpose doesn't it?
 

chem geek

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But what is the FC and CYA level in such pools that can't hold chlorine? If it's the "recommended by SWG manufacturers" 1-3 ppm FC with 60-80 ppm CYA, then that won't be enough to prevent algae growth so in that case using either a phosphate remove or an algaecide will slow down such growth so that the SWG can produce chlorine quickly enough. However, if such algae is killed off and then the FC maintained at a minimum of 5% of the CYA level, so 4 ppm FC with 80 ppm CYA for example, then algae growth can be controlled with chlorine from the SWG alone. You talk about selling them what they don't need, but they don't need phosphate removers if the FC level was set appropriately for the CYA level.
 

duraleigh

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Since this discussion is in THE Deep End, it's OK to continue. I hope there isn't a newbie who wanders over here and believes that phosphates is a problem in pools because it isn't.

Time and Time again, it has been proven that adequate chlorine is the answer to algae. We need to make sure our newbies don't lose sight of that fact.
 

chem geek

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swimcmp said:
If the swcg can't produce enough chlorine but you remove the phosphate then will maintain on its own seems to be a relationship between the two.
There is a relationship, but it is indirect. Phosphates are an essential nutrient for algae growth. So when phosphates are the limiting nutrient, higher levels will have algae grow faster thereby creating greater chlorine demand such that the SWG cannot keep up. However, this only happens when the active chlorine level isn't high enough to kill the algae faster than it can grow. If the FC is at least 5% of the CYA level in an SWG pool (7.5% in a manually dosed pool), then the chlorine kills green algae faster than it can grow regardless of nutrient level. This is because algae growth is ultimately limited by sunlight and temperature, taking 3-8 hours to double in population.

So you have a choice with the pools that you service. You can set an appropriate FC level for the CYA level and not worry about the phosphate level or you can use expensive phosphate removers and have a lower FC level. That's why I say that phosphate removers should be seen in the same vein as algaecides. They are supplemental products that are not necessary if one maintains the proper active chlorine level. Some municipal water districts have phosphates in their fill water so evaporation and refill will increase phosphate levels over time in that case so their removal is not always just a one-time treatment. The pool store in my local area services 2000 pools (a good portion of them SWG) with a target 4.5 ppm FC and they dilute the water when the CYA hits 100 ppm in the Trichlor pools. They aren't quite at a high enough FC for the CYA in the Trichlor pools so some of them get algae and they shock and use phosphate removers in those cases, but the SWG pools aren't a problem because their CYA level doesn't climb and their FC is high enough. As I wrote before, 4 ppm FC minimum with 80 ppm CYA works well for SWG pools.

Think of phosphates as fuels, such as wood, for a fire. The more wood in a fire, the more heat and fire there is. Think of chlorine as water that is dousing the fire. If you don't use enough water, then the fire can continue to burn albeit somewhat more slowly. If you use enough water on the wood, then a fire can't even get started because any spark or flame gets put out. The maximum size of the wood pile is limited by other factors so as long as you use at least the minimum amount of water on the wood for that maximum size of the wood pile, a fire cannot get started (i.e. algae growth cannot take off).
 

swimcmp

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If chlorine is 0 and I do mean 0, it doesn't make a bit of difference if cya is 1 or 100. This is what we have seen first hand. Phosphates over 2000 and unable to get a chlorine reading, once phosphates are lowered then we can get a chlorine reading, and then it makes the difference where the cya level is.
 

ping

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Simply put, you need to add more chlorine than the amount you put in. If the first dose doesn't register after an hour then you need another dose until the chlorine starts holding and the shock process is completed. The chlorine is being consumed by the organics and needs to be replaced. Turning a SWG to 100% is not going to do it, they are made for maintaining chlorine levels, not increasing them to shock a pool. I use liquid before parties to bump up a few points and afterwards to get back to my high end if needed.

You probably don't have the time to sit by a pool and do the shock process described here at TFP so you need to add the chemicals you can that allows you to not baby sit the pool. If you had the time, chlorine is all that you would need when the CYA is <100.
 
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