Phosphates.....are they worth removing??

[Swampwoman]

Saturn, I am holding out hope that my goofy pool will follow your example

Yes, re Jack's purple...talked to the tech at Jacks and it is phosphonic and has an agent for cleaning cell. That's why I chose it.

Aus, the Jack's isn't for cell cleaning...its for my metals and staining control. Right now I'm still riding .3 iron, and may get by without, (I'm now using softened water for top ups) but as soon as I get any kind of ph rise, its likely to be another story. Saturn and I are on well water, where you're darned if you do and darned if you don't on water replacement

Jacks purple contains diphosphonic acid combined with Hydroxyethylidene-1 to work in the high TDS environment of SWG.

 

[Saturn94]

Saturn, I am holding out hope that my goofy pool will follow your example

Yes, re Jack's purple...talked to the tech at Jacks and it is phosphonic and has an agent for cleaning cell. That's why I chose it.

Aus, the Jack's isn't for cell cleaning...its for my metals and staining control. Right now I'm still riding .3 iron, and may get by without, (I'm now using softened water for top ups) but as soon as I get any kind of ph rise, its likely to be another story. Saturn and I are on well water, where you're darned if you do and darned if you don't on water replacement

Jacks purple contains diphosphonic acid combined with Hydroxyethylidene-1 to work in the high TDS environment of SWG.

Sorry, I should have clarified I'm on city water.

I sent you a PM regarding SWCG use and staining as to not derail this thread.

 

[PAGirl]

Saturn, I am holding out hope that my goofy pool will follow your example

Yes, re Jack's purple...talked to the tech at Jacks and it is phosphonic and has an agent for cleaning cell. That's why I chose it.

Aus, the Jack's isn't for cell cleaning...its for my metals and staining control. Right now I'm still riding .3 iron, and may get by without, (I'm now using softened water for top ups) but as soon as I get any kind of ph rise, its likely to be another story. Saturn and I are on well water, where you're darned if you do and darned if you don't on water replacement

Jacks purple contains diphosphonic acid combined with Hydroxyethylidene-1 to work in the high TDS environment of SWG.

If you weren't on well water, would it have been easier to do a drain and refill to lower the phosphates, similar to lowering CYA?

 

[Swampwoman]

^Absolutely in my case with such high readings - I think....but maybe the cost of 600 lbs of salt would offset...I'm not used to being swg so that might make a difference.

For someone who wants to keep lower by a few thousand ppb, as insurance, the removal products may be a fit. But with extremely high numbers that are still extremely high, at $250 worth of product plus time vacuuming to waste repeatedly, i'd be inclined to think dilution/water change would normally be the way to go. (Remember in my case that $250 worth of product did NOT nail it and I'd need another $250. If there are still sequestrant products in my water breaking down daily, I could remove again and still have more...I am suspecting this is exactly what I've witnessed.)

I guess it would depend on water rates, cost of salt, and how much rebalancing would be involved. I suppose when you total salt cost together with everything else and water rate you could end up preferring removal if 2 gallons of Seaklear would do it.

I think the commercial gallon product exists for public recreational settings where both draining and low limits on chlorine are factors -- there it makes perfect sense as a solution to a 2-fold problem.

 

[Swampwoman]

Cell Life and Phosphate Longitudinal Study

This a.m. I calculated that based an average historical use of FC ppm per day in my pool (2.3) I should in theory get roughly 6.9 - 24-week seasons out of my T15 cell, which produces 1.47 lbs of chlorine gas at 100% run time and has a mfg lifespan of 580 lbs.

I'm going to track my cell-life over the next 7 years to see if my phosphate level interferes with both production and life span of this cell. Of course, the true experiment will be skewed by a liner change, but if I'm always using jacks purple even once my water is changed out, I predict I will still be accumulating 6,000 ppb per season.

Of course, there's a chance the experiment won't last a week, but right now its ticking along just perfectly, producing expected FC over the last 24 hours, etc. Touch wood

 

[Swampwoman]

UPDATE: Cell operating perfectly, producing exactly FC expected for run time base on daily output calculation, and no squaking to be cleaned.

Digging into more PO4 info with ProTeam at the moment but going to try to cross-reference the various things I'm being told by various Mfgs about phosphates before summary posting observations. Having trouble reconciling info about the volume of Polyphosphates added via metal sequestrants and potential breakdown into PO4.

A side observation...I don't think the pool industry actually did any research to come up with the magic 125 ppb ideal. I've now seen that number quoted as a limiter for algae in wetlands in some WQA material. I'm beginning to think this was borrowed

 

[Saturn94]

UPDATE: Cell operating perfectly, producing exactly FC expected for run time base on daily output calculation, and no squaking to be cleaned.

Digging into more PO4 info with ProTeam at the moment but going to try to cross-reference the various things I'm being told by various Mfgs about phosphates before summary posting observations. Having trouble reconciling info about the volume of Polyphosphates added via metal sequestrants and potential breakdown into PO4.

A side observation...I don't think the pool industry actually did any research to come up with the magic 125 ppb ideal. I've now seen that number quoted as a limiter for algae in wetlands in some WQA material. I'm beginning to think this was borrowed

Glad to hear the cell is working normally. I suspected it might.

 

[Austintatious]

Re: Added Phosphate Remover to SWG

So I noticed that the Pentair IC40 manual says that you should keep your phosphates under a certain amount.... I was higher and added remover... there is cheaper remover available at Lowes that is about 8 bucks to remove about 500 PPB in my pool... I know many here say the phosphates dont matter, but Pentair says otherwise.... It isnt THAT expensive to keep them down so until someone can explain to me why I shouldn't listen to Pentair, Im going to stay on top of them.

 

[Swampwoman]

Austin, we're trying to determine a "real world" level of concern in terms of theoretical phosphate scaling on salt cells, which no one in the industry actually has to date. While Pentair uses 500, its odd that Hayward doesn't I've had two different sources in the industry now tell me that they don't consider Pentair's guideline "real world"

For you, it may be easy to control phosphates and you're welcome to as you see fit - why not, as you say. You are fortunate because in some municipalities treated water has as much po4 as youre trying to limit This is actually an issue in water treatment plants and industrial boilers at the moment much more so than the pool industry.

For people on well water, who rely on maintaining a steady diet of metal control products that contain HEDP (diphosphonic acid, a polyphosphate with a baseline of orthophosphate to which chlorine ultimately reverts it over time) its another matter entirely. Its just not really possible to keep that low of a level when products like Jacks have you dosing to 10 - 12 ppm, which is 10,000 to 12,000 ppb of HEDP for maintenance

Historically, many TFP swg users has run at high po4 levels without problems.

Saturn here has been using Jacks purple for years and hasn't had issues. Right now, at extremely high levels, I am also running without problems...though keeping a close eye on the experiment

I think its fair to (prematurely?) conclude from my standpoint that a few other things are maintained before ever blaming phosphates for an swg problem, and several techs to date have agreed.

-- such as higher cya -- TFP recommends 70-80; run time adequate to maintain 5% of cya even when generator is off (for example, if you run 6 hours, that FC has to last you another 18 hours and remain above 5% of cya) etc.

One theoretical chemist in the industry who's posted on this subject rather extensively has pointed out that po4 removal as an algae-killing strategy isn't really possible/viable in and of itself because there are still organic phosphates in the water that are not removed by removal products such as lanthanum chloride.

So, the only "real" problem with phosphates chatter in the industry is that it currently distracts many pool owners from the actual simplest and most likely, science-based elements of algae outbreaks: a failure to maintain the FC:CYA ratio and control same through testing, or in the case of SWG, a failure to get run time, stabilization, and FC to the correct min. of 5%.

Instead, people are dosing their pools with a rare earth element that in itself can also be toxic (note: complicated, but not generally toxic in application because its insoluable when combines with phosphate) because a puck or swg mfg told them to, when 9 times out of 10, a failure to maintain this foundational sanitation ratio is actually the culprit.

That's why we care about what the truth is here...not that we'll necessarily find it

 

[JoyfulNoise]

Austintatious,

One thing to keep in mind is that "industry guidelines" are often written by industry interest groups, such as the APSP (Association of Pool & Spa Professionals) or the NPC (National Plasterers Council), and they are written for the benefit of that industry. The guidelines represent a uniform standard that all participants adhere to in order to limit the risk of liability and ensure a uniform code of action to be followed by all participants. Guidelines are NOT written for the benefit of the consumer.

If you ask Pentair why they chose that particular level of phosphates and what relationship that level has to the underlying scientific understanding of what phosphates do in pool water, you will get a blank stare and the rote response that it is the level that the APSP says it should be. There is little-to-no scientific basis for the numbers they choose.

Like the rest of us, you are free to put whatever you like into your pool water. I am currently experimenting with low phosphates as a method to reduce my FC/CYA ratio (I am trying to achieve 3%) given the other aspects of my pool that allow me to currently operate at the lower 5% level (I have an SWG and I use borates in my pool water). Hopefully this thread can shed some light on what, if any, benefit phosphate removers might have (very much TBD). As swampwoman pointed out in her response, there are plenty of situations where it would be costly to use phosphate removers on an on-going basis to achieve a low level simply because of other chemicals or fill water that continually raises PO4 levels. In those situations, the use of phosphate removers would be cost-prohibitive.

And a word of advice on "cheap" phosphate removers - be careful on the products you use. Many of the "cheap" removers have very low levels of lanthanum chloride in them and many come with clarifiers added to them (PhosFree is one such example). You could be paying far more than you realize for the cheap stuff on a per-oz basis than by using the higher concentration commercial grades and, since you have a DE filter, clarifiers are not a good idea. Clarifiers can cause DE to become "gummed up" on your filter grids making it very difficult to achieve a low clean pressure and harder to clean off during a tear-down. Most of the commercial grade phosphate removers are pure lanthanum chloride WITHOUT any additives to them.

 

[AUSpool]

A side observation...I don't think the pool industry actually did any research to come up with the magic 125 ppb ideal. I've now seen that number quoted as a limiter for algae in wetlands in some WQA material. I'm beginning to think this was borrowed

I found a water quality report a while ago with some phosphorus data but I didn't copy the link and had trouble finding it again. I'm glad I don't write things like that for a living. It has multiple values for total phosphorus given as default stressor triggers as 20 μg/L (20ppb) for upland rivers, 50 μg/L (50ppb) for lowland rivers, 10 μg/L (10ppb) for freshwater lakes and reservoirs, and 50 - 60 μg/L (50 - 60ppb) for wetlands. These are not limiting values but rather stressor trigger values where above the values it is likely to find changes in the normal species densities.

If there's a lack of chlorination in a swimming pool there are no population density changes its just green algae that dominates. I also found reference to a nitrate to phosphate ratio that is used as an indicator for blue green algae or Cyanobacteria where increasing the phosphate decreases the nitrate / phosphate ratio and favours Cyanobacteria over green algae.

I don't think that values from natrual systems can be easily adapted to chlorinated pools which are more like a closed system with no active bio mass. In a 10,000g pool at say 100ppb phosphorus there would be ~3.8g of phosphorus, if the 100ppb of phosphorus is used thats it, it's all used and being recycled through or within an algae bloom that would have a dry weight of ~500g. But in an active natural open system at 100ppb if the 100ppb is used it will still be at 100ppb the day after and a great deal more phosphorus is within the bio mass that is constantly being recycled.

While algal growth rate (or productivity) is related to the concentration of key nutrients in the water column, the biomass is more controlled by the total mass of these nutrients available to the growing algae (Wetzel 1975). In many cases, the water column nutrient concentration is not a good indicator of algal biomass. For example, the net water column nutrient concentration could be quite small in an ecosystem with a high algal biomass but with rapid nutrient cycling.

http://www.environment.gov.au/syste...1dde09e96ef/files/nwqms-guidelines-4-vol1.pdf
Table 3.3.2; 3.3.4; 3.3.6; 3.3.8.

 

[Swampwoman]

Weekly update on swg cell life in high phosphates:

Cell remains fully operational @ 3200 ppm salt

FC 6 (keeping it there due to potentially reactive water re phosphates)
Ph 7.5
TA 100 (this is higher than last week by 10...no explanation)
CH 90 (this is lower than last week, by 10, no explanation)
CYA 70ish
Iron .4 (slightly higher than last week by .1)
Temp 88 (heater is on, obviously)
Csi - -.66

Water is crystal clear
Reduced ph once when it reached a bit over 7.8...did acid demand test, 2 drops to 7.4

Faint iron staining on steps...not too bad...have not added Jacks Magic Purple and won't until I see I need it...want to read PO4 again when I get more distilled water and have time (eg next weekend) and don't want to skew test.

- - - Updated - - -

Thanks, Aus...will try to dig up where I found the 125 reference and post. Distracted by gardening, which of course requires adding, not removing, phosphorous I've considered whether or not the terrace, which is higher than pool, is a contributor to po4 in my setting

 

[JoyfulNoise]

SW,

You should up your CYA to 80ppm and let your FC drop down a bit to stay above the minimum FC of 4ppm (5% ratio). The higher CYA will allow you to hold onto the chlorine you produce better. By running at a 10% ratio, you are increasing your FC loss (and running your cell more than you have to) because the HOCl/OCl- concentrations are higher. I really think you have little to worry about in terms of algae and even if it did start to get a hold I'm certain you'd be diligent enough to see it right away and know exactly what to do. A 40% FC/CYA SLAM ratio is really only needed to clear green/black swamps. For a pool that has gone slightly cloudy, a lower ratio works just fine for a SLAM albeit it will work slower. I only say that to ease any fears you might have in increasing your CYA. We hear the mantra that high CYA is bad so much that it gets ingrained into our heads and makes it harder to raise it when it's appropriate to do so. In your case, now that you have an SWG, using more CYA to help lower the daily FC loss is an good thing to do as it will let you run the cell less. Running the cell less will keep the pH rise down and lowering your FC to get closer to 5% will help keep the metals in solution and sequestrants you use from breaking down faster.

Up to you.

Oh, and you might add a bit more CH to the water to get your CSI within range. I know you have to ride your pH lower for metals so adding a little CH will not hurt.

 

[Swampwoman]

^my "intended ch" was supposed to b higher. I had added enough 25 lbs) to get to around 130. Highest reading was 110...then 100 and now 90 all in a 2-week span. Not sure where ch is going, unless leftover sequestrant from last year is carrying it out. Reluctant to add more at $40 a pop until I figure out what's up with these results

Re: cya...the only reason I targeted 70 instead of 80 was in case I immediately had to switch back to mannual chlorine if swg ran afoul. May wait another week but intend to raise to 80. Also intend to run FC a wee bit lower in another week, but titrating down slowly as spring debris load here is heavy and I wanted to see how consumption went with water at my normal 88 degrees, which I just upped on weekend

 

[JoyfulNoise]

Gotcha. Same boat - I want to lower my FC to 3 but it's stuck at 5.5 and I'm already bottomed out at 3 hours pump run time and 50% on the SWG. I don't want to go lower so I may just wait until the water warms up and the bather load increases. I'm already using less energy to create chlorine than I did last year at this time.

Also, I believe your sequestrants are going to interfere with the CH test. They will bind up Ca2+ ions and possibly interfere with the dyes ability to hold Ca ions. You might want to call Taylor and ask them what the expected interference might be. So best not to add any additional CH until you know for sure.

 

[Saturn94]

SW,

You should up your CYA to 80ppm and let your FC drop down a bit to stay above the minimum FC of 4ppm (5% ratio). The higher CYA will allow you to hold onto the chlorine you produce better. By running at a 10% ratio, you are increasing your FC loss (and running your cell more than you have to) because the HOCl/OCl- concentrations are higher. I really think you have little to worry about in terms of algae and even if it did start to get a hold I'm certain you'd be diligent enough to see it right away and know exactly what to do. A 40% FC/CYA SLAM ratio is really only needed to clear green/black swamps. For a pool that has gone slightly cloudy, a lower ratio works just fine for a SLAM albeit it will work slower. I only say that to ease any fears you might have in increasing your CYA. We hear the mantra that high CYA is bad so much that it gets ingrained into our heads and makes it harder to raise it when it's appropriate to do so. In your case, now that you have an SWG, using more CYA to help lower the daily FC loss is an good thing to do as it will let you run the cell less. Running the cell less will keep the pH rise down and lowering your FC to get closer to 5% will help keep the metals in solution and sequestrants you use from breaking down faster.

Up to you.

Oh, and you might add a bit more CH to the water to get your CSI within range. I know you have to ride your pH lower for metals so adding a little CH will not hurt.

Is CSI below -.6 an issue with vinyl pools? Pool math only indicates it's an issue with plaster pools.

- - - Updated - - -

Gotcha. Same boat - I want to lower my FC to 3 but it's stuck at 5.5 and I'm already bottomed out at 3 hours pump run time and 50% on the SWG. I don't want to go lower so I may just wait until the water warms up and the bather load increases. I'm already using less energy to create chlorine than I did last year at this time.

Also, I believe your sequestrants are going to interfere with the CH test. They will bind up Ca2+ ions and possibly interfere with the dyes ability to hold Ca ions. You might want to call Taylor and ask them what the expected interference might be. So best not to add any additional CH until you know for sure.

Interesting, I didn't know the sequestrant would (might?) interfere with CH testing. It would be nice to confirm.

 

[JoyfulNoise]

Is CSI below -.6 an issue with vinyl pools? Pool math only indicates it's an issue with plaster pools.

It's not a problem for vinyl, but I always prefer to counsel people to try to stay within ranges where possible. CH below 100ppm, even in a vinyl pool, seems quite low to me. Not that it matters much, but I think the water would feel too soft....but maybe that's because I live in desert where taking a shower in 300ppm+ CH water hardness is a bit like showing in portland cement

Interesting, I didn't know the sequestrant would (might?) interfere with CH testing. It would be nice to confirm.

Yes, there is a great likelihood of interference. There are actually three chelation processes occurring -

1. The Eriochrome Black dye used in the test "grabs" the Ca²⁺ ion from the water, this is what causes the dye to change from blue (it's normal color in water with no calcium) into reddish-purple.

2. Any phosphonate sequestrant around will "grab" lots of calcium as that it what it is best at. The phosphonate is likely a stronger chelating agent then the Eriochrome Black dye.

3. The EDTA titrant is used to strip the calcium from the dye and hold it. This is what causes the solution to change from reddish-purple back to light blue.

So, it all depends on which chelating agent is stronger and the chelation strength is usually pH dependent. One way to deal with sequestrants in water testing is to do an acid-digestion step first. One typically uses a strong acid like nitric acid which is also an oxidizer. This destroys any sequestrant in solution and releases the ions captured by it. Then, the pH is usually adjusted back up to the normal range (although you have to be careful not to cause scaling) and testing is performed as usual. A call to Taylor will likely confirm if there is any interference in the CH test form HEDP (I suspect there is) and what can be expected. In my pool water with 850ppm CH, the interference would likely be minimal but, in Swampwoman's pool, the CH is so low that the interference might be a larger fraction of the overall CH value.

 

[Saturn94]

It's not a problem for vinyl, but I always prefer to counsel people to try to stay within ranges where possible. CH below 100ppm, even in a vinyl pool, seems quite low to me. Not that it matters much, but I think the water would feel too soft....but maybe that's because I live in desert where taking a shower in 300ppm+ CH water hardness is a bit like showing in portland cement



Yes, there is a great likelihood of interference. There are actually three chelation processes occurring -

1. The Eriochrome Black dye used in the test "grabs" the Ca²⁺ ion from the water, this is what causes the dye to change from blue (it's normal color in water with no calcium) into reddish-purple.

2. Any phosphonate sequestrant around will "grab" lots of calcium as that it what it is best at. The phosphonate is likely a stronger chelating agent then the Eriochrome Black dye.

3. The EDTA titrant is used to strip the calcium from the dye and hold it. This is what causes the solution to change from reddish-purple back to light blue.

So, it all depends on which chelating agent is stronger and the chelation strength is usually pH dependent. One way to deal with sequestrants in water testing is to do an acid-digestion step first. One typically uses a strong acid like nitric acid which is also an oxidizer. This destroys any sequestrant in solution and releases the ions captured by it. Then, the pH is usually adjusted back up to the normal range (although you have to be careful not to cause scaling) and testing is performed as usual. A call to Taylor will likely confirm if there is any interference in the CH test form HEDP (I suspect there is) and what can be expected. In my pool water with 850ppm CH, the interference would likely be minimal but, in Swampwoman's pool, the CH is so low that the interference might be a larger fraction of the overall CH value.

I sent you a PM as not to stray off topic here.

 

[AUSpool]

Weekly update on swg cell life in high phosphates:


Cell remains fully operational @ 3200 ppm salt


Thanks, Aus...will try to dig up where I found the 125 reference and post. Distracted by gardening, which of course requires adding, not removing, phosphorous I've considered whether or not the terrace, which is higher than pool, is a contributor to po4 in my setting

I wish I could run my cell at 3200 ppm.

Given your high po4 I doubt a little more coming from the garden in heavy rain would make much difference. But it would be adding nitrates, one of the other significant nutrients for growth. Having quantified or attempted to quantify the growth from a given amount of phosphate it occurred to me that the term 'limiting' may not be the most appropriate where I think 'significant' is probably better suited.

Using the term 'significant' and given an appropriate availability of other nutrients and growth factors I don't think 20-30ppb of po4 would 'fuel' a significant algae growth. At 100- 125ppb of po4 I don't think growth in terms of mass would be significant either but I can't quantify that. I suspect that a significant growth would begin somewhere above 100ppb, maybe in the range of 100 - 300ppb po4.

I used a percentage of dry weight of phosphorus (~0.75%) for total mass of micro organisms to calculate a theoretical dry mass of algae for 100ppb of po4 in 10,000g (38,800L). I figured it would be ~500grams dry mass of algae but have no idea what 500g of hydrated algae cells would look like in a 10,000g pool. Somewhere between just a little cloudy to full blown bright green.

 

[Swampwoman]

Weekly Update on Cell Life in High Phosphates

I'm a day early, but I'm gonna start reporting on Sundays when I have time to fiddle with the PO4 Meter, vinegar, distilled water, etc.

First, readings:

FC 4 (Id dialed down a little more than I'd meant 2 days ago, put back up to 15%)
CC 0
Ph 7.6 - unadjusted ths week
TA 100
CH - ran out of reagent. Next week will test by adding 6 drops of r12 to nx the metal net reference
CYA - 70 ish (haven't added more yet)

Salt - swg said 3300...suspect some concentration with evaporation this week as water heated/temps low

Pump was at 20 psi, 25% above clean pressure...backwashed...surprised at rust colored-iron in backwash bubble. Calcium pulling? No idea.

WAG Theory on Phosphate Level Perpetual Production Machine -

Today's reading with Hanna meter, careful 50/50 dilution, etc...wait for it:

51,000 ppb or 51 ppm po4!

This is a net increase of 11,000 ppb from 40,000 ppb tested on April 30th.

1. I have not added ANY sequestrant of ANY kind this year since opening.

2. I have faint iron staining starting on my steps, which usually means "active" sequestrant is wearing off/needs top up

3. I am beginning to suspect that sequestrant takes much longer to degrade from a polyphosphate to po4 than I originally thought

4. I believe that the Seaklear 2-gallon treatment did in fact drop my po4 level as expected, and quite possible to the order of the predicted 36,000 ppm anticipated, but since it'd taken 2 more weeks to find a confirming/accurate way to test, the previous sequestrant simply continued to degrade.

AND

5. In my case and others like me, it would be entirely cost prohibitive to rely on phosphate removes to address high volumes of spent sequestrant.

At the same time, I'm REALLY not sure it matters one whit.

Cell is running like a champ.

End STARLOG