Will Phosphates increase chlorine demand?

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benavidescj

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Apr 27, 2010
431
Fleming Island, FL
JasonLion said:
1) Don't assume it will be a short time, if you are not adding enough chlorine it can be a very long time. And don't assume that the SWG will ever catch up on it's own. You need to raise the FC level up to measurable levels by manually adding chlorine, how ever much chlorine that takes.

I did not assume it would be a short time, I was just going by what Chem Geek said just below your post above, "If there was leftover ascorbic acid, then that would certainly create a chlorine demand, but it would be very fast so you wouldn't be able to add chlorine and pass the overnight chlorine loss test." Every day I would add enough chlorine to get up to 8 to 9 ppm. No loss overnight, but no gain either. Never went below 3 ppm except for that 24 hours during the AA treatment at which time I had 2 quarts of polyquat in the pool.

I also did not assume that the SWG would ever catch up. I am aware that if I get close to the lower FC limit I have to manually dose. I was manually dosing up to 8 to 9 ppm during the three weeks that this was occurring. Never did I just let the SWG try to catch up.

JasonLion said:
3) Then you had a low level algae problem, presumably started because you failed to raise FC levels quickly enough after the AA treatment. The period after an AA treatment is a balancing act. You can't add chlorine too quickly, nor can you add chlorine to slowly. You have to establish a minimal FC level by the second or third day or you are certain to get algae (which may or may not be visible). And once you get algae it is common for the SWG to be unable to deal with it on it's own.

I thought I had an algae problem also, that is why I did an overnight test three times over three nights. CC was .2 or 0, water has been clear the whole time this has gone on and <1ppm loss overnight. Remember I had 2 quarts of polyquat in the pool during the 24 hour AA treatment. I then added 5ppm chlorine after 24 hours.
 

JasonLion

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Perhaps I have been misunderstanding something. The amounts of chlorine you added don't really mean anything, but if you passed an OCLT that suggests my interpretation is wrong. But I don't understand how that fits with "I am talking about not producing chlorine for three weeks", what were you measuring that lead you to that assumption if you had measurable chlorine levels?

Is there any chance you had the SWG on when you were passing the OCLT?
 

benavidescj

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Apr 27, 2010
431
Fleming Island, FL
JasonLion said:
Perhaps I have been misunderstanding something. The amounts of chlorine you added don't really mean anything, but if you passed an OCLT that suggests my interpretation is wrong. But I don't understand how that fits with "I am talking about not producing chlorine for three weeks", what were you measuring that lead you to that assumption if you had measurable chlorine levels?

Is there any chance you had the SWG on when you were passing the OCLT?

For the three weeks I was manually dosing because the SWG was obviously not keeping up if producing at all. I was checking my chlorine 1 or 2 times per day because I was worried about dropping below minimums. During the three weeks I was trying different things. One of the things I tried was running the SWG 24 hours. I checked the chlorine level in the evening and by morning I had not gained any. When I was actually doing an overnight test I had the system off.
 

chem geek

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Mar 28, 2007
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OK, what you have written is more consistent with scaling on the plates. This can happen with high CH and phosphate levels especially if the pH isn't kept lower or buffered with 50 ppm Borates.

What were your pH, TA CH and phosphate levels when the chlorine generator could not seemingly produce chlorine?
 

benavidescj

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Apr 27, 2010
431
Fleming Island, FL
chem geek said:
OK, what you have written is more consistent with scaling on the plates. This can happen with high CH and phosphate levels especially if the pH isn't kept lower or buffered with 50 ppm Borates.

What were your pH, TA CH and phosphate levels when the chlorine generator could not seemingly produce chlorine?

I thought about that also, and after about two weeks of the no chlorine issue I took the cell off the line and cleaned it. It was pristine before I started and there where no bubbles at all during the process.

Here are my levels taken during the three weeks:

Test Results:
Water: clear
FC: 4
CC: .2
CYA: 70
TA: 70
Salt: 3400
CH: 300
 

benavidescj

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Apr 27, 2010
431
Fleming Island, FL
chem geek said:
There wouldn't be any bubbles from the cleaning because the scale wasn't calcium carbonate and it's the carbonate that bubbles with acid forming carbon dioxide. Do you know the pH and the phosphate level?

The pH dropped to about 6.8 during the AA and I slowly brought it up to 7.2 over three days and phosphate approx 1000 - 1500ppb. Right now the pH is 7.5. Borate level is about 10.

After cleaning the cell I was not getting any chlorine in the pool. I think I called the technician about 3 days after cleaning the cell. I cleaned the cell about 5 days before adding the phosphate remover.
 

Swampwoman

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Apr 27, 2012
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Grand Rapids, MI
I for one will be interested in hearing the results of your experiment because I suspect you're on to something.

I use Jack's Magic Pink Stuff weekly at a does of 16 oz. for my 22k pool to maintain iron sequestering. It is comprised of diphosphonic acid (forgive me if I've spelled it wrong ;)
I SWEAR my chlorine demand fluctuates by as much as net 20%-30% or more until the Jack's wears down and I'm ready for another dose. Eg. Normal dose was previously to about 7 to maintain min. 4 safely (now 3- 3.5ish with cya splashout) with about 2 ppm per day actual demand. Since maintaining on Jack's I'm seeing more like 3 - 3.5 ppm demand. No other signs of algae; have not have even a fraction of a .cc for literally weeks; water is crystal clear, etc.

My empirical evidence suggests to me that sequestering metal/fighting stains et al will simply require higher chlorine demand as a by-consequence.

However, now you've got me thinking perhaps I should try to remove the "spent" phosphates of the sequestrate, provided that doesn't somehow interfere with keeping the iron in solution. This is my first year at pool maintenance, so if that's something I *should* be doing, feel free to chime in. - Would TSP cause the iron to drop out of solution, or is it that the actual phosphates are only generated as the diphosphonic acid is spent???
 

chem geek

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Swampwoman said:
Would TSP cause the iron to drop out of solution, or is it that the actual phosphates are only generated as the diphosphonic acid is spent???
The orthophosphate is released when the HEDP is broken down slowly by chlorine.

What is strange is that there are others with SWCG pools that get by just fine with high phosphate levels. So if there is something going on with phosphate and SWCG, it isn't consistent. Maybe there are some specific SWCG plate coatings that have a problem with phosphate in the water. The experiment will be interesting to see.
 

JamesW

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Mar 2, 2011
28,291
I think that it would be helpful if the salt system could be analyzed to see if it was actually producing, or not. Did the cell show any error lights?

There are several ways to determine if the cell is working:

1) Test the water coming out of the return while the cell is set to 100 % to see if the FC level is higher than in the main pool water.
2) Look for hydrogen bubbles coming out of the return.
3) Monitor power usage by the salt system (voltage and current).

Note: I know that you said

I had Pentair come out and check the unit and they stated that the unit was producing chlorine just fine
However, the unit might be inconsistent, and perhaps it was working when checked, but not later.
 

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benavidescj

LifeTime Supporter
Apr 27, 2010
431
Fleming Island, FL
JamesW said:
I think that it would be helpful if the salt system could be analyzed to see if it was actually producing, or not. Did the cell show any error lights?.

The cell lights were all green the entire three weeks. My understanding of what the tech did (I was not there, but asked) is that he took the cell off the line and inserted it into a bucket with salt water. He then turns it on and checks the chlorine level of the resulting water.

I took samples from the return and did get a higher chlorine reading then the rest of the pool. For instance if the pool was 8ppm the return was reading 8.5 ppm. I don't know what the differential should be between the pool and the returning water, but .5 sounds rather low. I also looked for bubbles but did not see any. I don't ever recall seeing bubbles from my returns even when the cell was working fine, but I don't recall looking specifically for that before either.
 

benavidescj

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Apr 27, 2010
431
Fleming Island, FL
Ok, I went out and bought some more sequestering agent. The sequestering agent I used before is called Suncoast Chemicals Salinity Stain Control. It is just phosphoric acid. My plan is to add the whole bottle (1 qt) like I did before. If that does not do anything I am going to drop the pH down to 6.8. Dropping the pH down to 6.8 is simulating what the AA treatment did. I know this is not exactly what was done before, but I do not want to go buy more ascorbic acid right now due to expense.

If adding the sequestering agent and dropping pH down to 6.8 does not do anything then I will add polyquat and drop the FC down to 0 again.

If anyone sees any issues with this procedure let me know. I won't start it for another couple of days.
 

Swampwoman

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Just FYI, with Jack's Pink I know it's 32 oz PER 10,000 GALLONS. You'd need 2.8 bottles to be at effective sequestrate.

What does the product you're using say is a full dose? I'd be pretty surprised if it were just 1 qt.
Just my .02
 

benavidescj

LifeTime Supporter
Apr 27, 2010
431
Fleming Island, FL
Swampwoman said:
Just FYI, with Jack's Pink I know it's 32 oz PER 10,000 GALLONS. You'd need 2.8 bottles to be at effective sequestrate.

What does the product you're using say is a full dose? I'd be pretty surprised if it were just 1 qt.
Just my .02

You are correct that one bottle (1 qt) is only good per 10,000 gallons per the instructions on the bottle. When I went to the store to pick it up the guy told me I did not need to go by the instructions on the bottle. He said they have a chart that they go by that tells them how much to put in. He told me that I would be fine with the 1 qt. I don't know if what he was telling me was true, but he sounded like he knew what he was talking about. In the end the stains did not come back, but who knows, they may not have come back even if I did not put anything in the water.

By the way, the stuff they sold me (Suncoast Chemicals Salinity Stain Control) is manufactured by Jack's Magic. Says it right on the back of the bottle.
 

Swampwoman

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Apr 27, 2012
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LOL, I guess JM is private-labeling ;) I know Haviland/ProTeam is doing the same thing for a local franchise. It always irks me a bit because I want the MSDS sheets to know what I'm getting!

Well, I will say that I found Jack's effective at their recommended rate of dosage and less effective/not effective enough on iron at a lower than prescribed dosage, but YMMV ;)
 

benavidescj

LifeTime Supporter
Apr 27, 2010
431
Fleming Island, FL
First step of testing completed.

Added phosphates using Suncoast Chemicals Salinity Stain Control. As near as I can tell the current level of phosphates is approx 2000 ppb. I had to dilute the Taylor K-1106 test 4 to 1.

NO noticeable increase in chlorine demand with this one step.

Next step is to drop pH down to 6.8 to simulate the addition of ascorbic acid.

Current numbers:

water is clear
pH 7.48
FC 8
CC 0
TA 70
CYA 70
Borates <10
CH 310
phosphates approx 2000
Salt 3800
 

benavidescj

LifeTime Supporter
Apr 27, 2010
431
Fleming Island, FL
Second step of testing completed.

Dropped pH down to 6.8

NO noticeable increase in chlorine demand with this step.

Next step is to add polyquat. Using the same thing I did before Suncoast All In One Algaecide. Composition is Poly [oxyethylene (dimethyliminio) ethylene (dimethyliminio) ethylene dichloride] 60%, inert 40%.

Current numbers:

water is clear
pH 6.8
FC 8
CC 0
TA 70
CYA 70
Borates <10
CH 310
phosphates approx 2000
Salt 3800
 

JasonLion

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Polyquat will consume some chlorine, but it shouldn't be all that much.

Swampwoman, the required dosage of a sequestrant depends on the metal level you are trying to sequester. More metals in the water means you need to use more sequestrant. Jack's instructions are for some "typical" level of metals, but the actual dosage requires varies all over the place, depending on the situation.
 

benavidescj

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Apr 27, 2010
431
Fleming Island, FL
I think adding the polyquat may have done it. I used Suncoast All In One Algaecide. Composition is Poly [oxyethylene (dimethyliminio) ethylene (dimethyliminio) ethylene dichloride] 60%, inert 40%.

I did not have to add chlorine through the whole test until last night when the FC fell to 3.5. FC was holding with the SWG at around 8. I added two 182oz jugs to bring the FC up to 8.5 last night.

I am now loosing about 3-4 ppm FC per day after adding the poly.

I will monitor closely over the next few days and take readings 2 hours after adding FC, morning and evening.

Current numbers:

water is clear
pH 7.4 (rose naturally)
FC 4.5
CC 0
TA 70
CYA 70
Borates <10
CH 310
phosphates approx 2000
Salt 3800
 

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