Pool consuming massive amounts of FC and CYA

[Rasalon]

Greetings!

I have a 25,000 gallon salt water pool with a solid electric cover, solar heat and a 60 square foot DE filter. Last year never had an issue with the pool. I kept the SWG at 20% generation all summer, and everything was stable.

Because of the electric cover, which I keep closed at nights and when not at home, I never have an issue with evaporation or rain water contamination, so never have to add/subtract water, except when I backwash the filter. The pool is controlled by a Pentair Intellitouch, so the temperature from the solar is kept pretty constant, so I don't have wild temperature swings.

Over the past 3 weeks I cannot raise my FC above 0 and my CYA above 40. I use the TF-100 test kit, along with a LaMotte digital pH and TDS meter. I have been running the SWG generator at 100% for 3 weeks (a lot of chlorine bubble activity in the SWG cell, so I know the cell is working), adding almost one gallon of bleach per night for 2 weeks straight (15 gallons of 6% Chlorox regular bleach added total), 4 pounds of di-chlor shock, and adding 6 pounds of CYA per week (18 pounds 100% pure CYA total). Water is crystal clear.

Here are my latest readings from the TF-100 and other methods:

FC - 0.0 (tested using TF-100 chlorine drop test, verified with test strips)
CC - 4.0 (tested using TF-100 chlorine drop test, TC verified with test strips and Taylor pH tester)
pH - 7.1 (tested using Taylor test kit and LaMotte pH tester - a bit low, but I just brought the TA down)
TA - 110 (tested with TF-100 TA test)
CH - 360 (tested with TF-100 CH test)
CYA - 40 (tested with TF-100 CYA test, verified with test strips)
Copper - 0.3 ppm (tested with test strips)
Iron - 0.0 ppm (tested with test strips)
Phosphates - 1000 bbp (tested with test strips)
Salt - 3800 ppm (tested with LaMotte TDS digital tester, calibrated at the beginning of the pool season)

Why can I not get my FC to budge all of a sudden, even with the SWG at 100% and having added 15 gallons of bleach? Next, why can't I get my CYA to budge, even after 18 pounds of pure CYA? My pH was at 7.8, and my alkalinity at 140, so I added muriatic acid last weekend, which got my TA and pH down, but still can't control FC or CYA.

What do I need to do to adjust, and in what order? Any help is appreciated, as I am getting quite frustrated this time around.

Also, other than adding the shock this one time, the only chemicals I add to the pool are bleach, muriatic acid, cyuranic acid, and iron free softener salt. I don't use any algacide, pool additives, etc. Thank you.

 

[JasonLion]

FC will behave like that if there is ammonia in the water. Ammonia can come from CYA breaking down or from fertilizer getting into the pool. There are also rumors of a bad batch of CYA, that doesn't actually contain CYA, though not enough to be sure of it.

I suggest adding much larger amounts of chlorine at one time. Raise the pool up to shock level in the evenings, test and adjust back up to shock level a couple of times each evening if you can manage it. If you can, get an ammonia test and measure the ammonia level. Don't worry about the CYA level again until you can maintain an FC level overnight with a loss of 1.0 or less.

 

[zea3]

What Jason said, plus you may want to dial the SWG % back down. Running it at 100% will shorten the cell life, and it is not currently creating chlorine fast enough to clear whatever is in your water. Use the liquid chlorine to keep the pool at shock level until you have passed the overnight test.

 

[Rasalon]

FC will behave like that if there is ammonia in the water. Ammonia can come from CYA breaking down or from fertilizer getting into the pool. There are also rumors of a bad batch of CYA, that doesn't actually contain CYA, though not enough to be sure of it.

I suggest adding much larger amounts of chlorine at one time. Raise the pool up to shock level in the evenings, test and adjust back up to shock level a couple of times each evening if you can manage it. If you can, get an ammonia test and measure the ammonia level. Don't worry about the CYA level again until you can maintain an FC level overnight with a loss of 1.0 or less.

Thank you for the quick reply. Over what period should I add the chlorine, and is there an upper limit? My supermarket had a sale this week on 1.5 gallon bottles of Chlorox (I bought 10 bottles), and I have been adding a bottle every hour this evening (4.5 gallons added this evening so far).

Also, do you have a recommendation for an ammonia test kit? After searching, they seem to be targeted towards fish aquariums, and they have both fresh water and salt water. Do I aim for a salt water ammonia test kit? And if my ammonia turns out to be high, what do I do about it?

Thank you again.

 

[JasonLion]

If the ammonia level is really high, it is often worth replacing a lot of the water, rather than using the massive amounts of chlorine it takes to burn that much ammonia off.

In a 25,000 gallon pool with CYA around 40, you can add as much as 6 gallons of 6% bleach at a time (remember most bleach jugs are not gallon jugs), wait an hour, and if the FC level is still zero, repeat.

 

[Rasalon]

If the ammonia level is really high, it is often worth replacing a lot of the water, rather than using the massive amounts of chlorine it takes to burn that much ammonia off.

In a 25,000 gallon pool with CYA around 40, you can add as much as 6 gallons of 6% bleach at a time (remember most bleach jugs are not gallon jugs), wait an hour, and if the FC level is still zero, repeat.

Thanks, any recommendations on an ammonia test kit for a salt water pool?

 

[frustratedpoolmom]

Ammonia test kits can be purchased at pet stores.

 

[Rasalon]

I will be hunting up pet stores for an ammonia test kit over the next few days.

If it turns out I have ammonia in the pool, what ratio of water replacement should I do? 30%? 50%?

Just when I think I have this pool maintenance down, another variable is thrown in. Thanks to everyone for their help.

 

[Rasalon]

As a follow up, I bought ammonia test strips today, and tested the pool for ammonia. It barely registered any ammonia, but I think that may have been the issue as all my symptoms matched and I couldn't define the issue until the tail end.

I added 6 gallons of bleach last night, and shortly after, FC was back down to zero. However, I added another 6 gallons this evening, and almost 2 hours later, FC is over 10. This is the first time in over 3 weeks I finally have a FC reading, so am excited.

I will check the FC tomorrow morning, and set my SWG to maintain 4ppm of chlorine. Once steady, I will then work on getting CYA back up. Thanks for all the help, I hope I am out of the woods.

 

[chem geek]

You are probably over the hump, but there can still be extra chlorine demand for a while that isn't quite so rapid at consuming chlorine. Nevertheless, it does appear that the worst is over. Just keep an eye on the chlorine level to make sure the SWG can keep up and if it can't, supplement with chlorinating liquid or bleach until it can.

 

[Rasalon]

Just wanted to post an update to this, and see if I can also get some additional opinions.

First off, my pool chlorine problem has been solved, took 45 gallons of bleach over a week to finally get FC to hold for 24 hours. FC has been holding steady at around 4 to 5 for two weeks now.

Secondly, my CYA problem has been solved. It took 32 pounds of 100% CYA to get my stabilizer reading at 70.

I am now working on getting my total alkalinity down by adding acid to get pH down to 7.0, then aerating with a 1/4HP submersible pump connected to a nozzle, which is sprays halfway across the pool. I aerate until pH gets back up to 7.4 to 7.5 (usually about 18 to 24 hours), then add acid again. Been doing this for a few days, gone through 6 gallons of acid already.

Here are my current readings:
- FC: 4 (using TF-100 and pool test strips)
- TC: 4 (using TF-100 and pool test strips)
- CYA: 70 (using TF-100), 60 - 100 (using pool test strips)
- CH: 300 (using TF-100 and pool test strips)
- TA: 110 (using TF-100 and pool test strips)

This is a 25,000 gallon pool with a SWG.

So my current questions:

- Why is my pool consuming massive amounts of chemicals? 32 pounds of 100% pure to raise CYA to 70 is unheard of. I bought three different brands of CYA in case one was being ineffective. And so far I used 6 gallons of 31.45% muriatic acid (sealed bottles with recent date codes from Home Depot) just getting my TA down from 180 to 110.

- In order to keep my pool at 4 of FC, I run my SWG 22 hours a day at 75% plus have a chlorine tab in each skimmer. Where is my chlorine going? This pool has a solid electric cover, so when it it closed during wind/rainstorms, or at night when I am not aerating, the pool is very well sealed from anything entering or water evaporating. The SWG is working, because if I place a pool test strip in front of the outlet, the strip goes dark purple, in the 10 to 20 FC range. With the SWG generator running, it doesn't even make sense that I had to add 45 gallons of bleach.

- While lowering TA, and having a low pH around 7.0 to 7.2, is this consuming the chlorine or making it ineffective?

As a reference point, last year I had the SWG running at 10% for 8 hours a day, and my FC held at about 6.

Also, wanted to add, I am lowering the TA so I can get started on adding borates. I bought more than enough Borax (had to buy out the complete stock from 4 stores), but now have enough, along with the acid,

Any insights appreciated, at least the pool is stable, but need to figure out why the massive chemical consumption. Thank you.

 

[chem geek]

I had the bacterial conversion of CYA into ammonia happen to me as I described in this thread that took around 56 ppm FC cumulatively added in my case, but I caught the problem very early on. You have added 111 ppm FC cumulatively (from 45 gallons of 6% bleach) before the chlorine started to hold (though it sounds like you are using the SWG so really the chlorine isn't holding yet if it still drops overnight > 1 ppm if the SWG isn't on).

When bacteria convert CYA into ammonia, for every 10 ppm CYA there is around 3 ppm ammonia that is produced and this can take from 24-30 ppm FC to get rid of. So you may have had 40-50 ppm CYA get converted to ammonia in your case, maybe more.

If you were adding CYA before you were registering non-zero FC (and that sounds like what you were doing), then the added CYA would have just fed the bacteria to have more converted into ammonia. 32 pounds of pure CYA in 25,000 gallons would normally raise the CYA by 153 ppm.

At this point, I suspect that you have gotten rid of the ammonia, but that there is still partially oxidized CYA that is accounting for the high chlorine demand. That should drop off over time, but I'd keep the FC up higher to accelerate this process (this will also kill off any nascent algae growth that might still be present). If you don't want to go to shock levels (28 ppm), then at least have the FC higher, say at 10 ppm, until your overnight FC loss (with the SWG off during that time) is <= 1 ppm.

The 6 gallons of full-strength Muriatic Acid (31.45% Hydrochloric Acid) should lower the TA by 120 ppm though you only saw a drop of 70 ppm. Are you sure that your pool isn't larger than 25,000 gallons (say, 40,000 gallons, though that does seem extraordinarily large)?

Richard

 

[Rasalon]

I had the bacterial conversion of CYA into ammonia happen to me

Thanks for the reply. I have been using ammonia test strips for about 3 weeks (from a pet store for ammonia testing in an aquarium, and it has both fresh water and salt water readings), and my ammonia has always been close to zero.

At this point, I suspect that you have gotten rid of the ammonia, but that there is still partially oxidized CYA that is accounting for the high chlorine demand.

Is there any way to measure this so I know what I am up against?

If you don't want to go to shock levels (28 ppm), then at least have the FC higher, say at 10 ppm, until your overnight FC loss (with the SWG off during that time) is <= 1 ppm.

So the process for this would bring FC up to 28 ppm, run the SWG during the day, turn off everything at night, and if FC drops below 28 the next morning, add enough chlorine to bring back up to 28 ppm, etc? Should I stop the process of currently trying to lower my pH? Also, 10 gallons of bleach will further lower my pH, do I need to add Borax at the same time to raise pH without completely undoing the TA lower I have completed?

Also, to get to 28 ppm, I would need to raise my FC by 24 ppm, since my FC is currently at 4. By my calculation, that would be about 10 gallons of bleach, correct?

Are you sure that your pool isn't larger than 25,000 gallons (say, 40,000 gallons, though that does seem extraordinarily large)?

I have my original construction and survey documents, they state 17' x 36' Roman pool (107' perimeter), 3' to 8' depth, 562 square feet of water, 23,750 gallons, so the math works out to be close. I just use 25K as an estimate, as it is easier.

Thanks again for the help, I hope to have this problem solved eventually!

 

[chem geek]

I have been using ammonia test strips for about 3 weeks (from a pet store for ammonia testing in an aquarium, and it has both fresh water and salt water readings), and my ammonia has always been close to zero.

You'd only measure the ammonia at the early stages when the FC was 0 and before you added a bunch of chlorine. You got your ammonia test after you had been hitting the pool hard with chlorine.

Is there any way to measure this so I know what I am up against?

You could do a bucket test where 1/4 teaspoon of 6% bleach in 2 gallons of pool water is 10 ppm FC and see how much it takes before the chlorine holds consistently not dropping by more than around 2 ppm FC in 24 hours (keeping the bucket out of sunlight -- a 1 ppm FC drop would be better, but could take longer). However, if the oxidation is slow, it can take some time before the chlorine demand drops, but at least you can raise the FC to shock levels (around 30 ppm) to see if this seems to accelerate the process to get the chlorine demand to drop more quickly. Usually the bucket test is more useful for figuring out the chlorine demand from the early stages when oxidizing ammonia and isn't as useful for the later stages that are slower.

So the process for this would bring FC up to 28 ppm, run the SWG during the day, turn off everything at night, and if FC drops below 28 the next morning, add enough chlorine to bring back up to 28 ppm, etc? Should I stop the process of currently trying to lower my pH? Also, 10 gallons of bleach will further lower my pH, do I need to add Borax at the same time to raise pH without completely undoing the TA lower I have completed?

Yes, that sounds reasonable, at least initially. Normally you don't run the SWG when shocking, but since we know you've got unusually high chlorine demand you can run the SWG during the day rather than have to manually add chlorine more frequently. As for your pH, you don't want that to rise too much so should add acid as needed. As for lowering the TA, that's up to you whether you want to wait on that or not -- just adding acid to keep the pH down should slowly lower the TA anyway. Yes, I would lower the pH first before shocking since the bleach will raise the pH (it won't lower it, as you described) and render your pH test useless until the FC is dropped again. Lower the pH to 7.2 before shocking with the bleach.

Also, to get to 28 ppm, I would need to raise my FC by 24 ppm, since my FC is currently at 4. By my calculation, that would be about 10 gallons of bleach, correct?

Yes, that's about right. 10 gallons of 6% bleach would raise the FC by 25 ppm. I assume you realize that bleach is usually not sold by the gallon. The containers are usually 96-ounces (3/4 gallon) or 1-1/2 gallon.

 

[Rasalon]

Yes, I would lower the pH first before shocking since the bleach will raise the pH (it won't lower it, as you described) and render your pH test useless until the FC is dropped again. Lower the pH to 7.2 before shocking with the bleach.

Ah, I thought bleach was acidic. So bleach will raise my pH. Does bleach also raise TA?

Yes, that's about right. 10 gallons of 6% bleach would raise the FC by 25 ppm. I assume you realize that bleach is usually not sold by the gallon. The containers are usually 96-ounces (3/4 gallon) or 1-1/2 gallon.

I buy my bleach from Target, it comes in something like 1.45 or 1.42 gallon containers, and is only $2.29 each, the cheapest I have found for the quantity I need.

Thanks again for the help!

 

[chem geek]

Ah, I thought bleach was acidic. So bleach will raise my pH. Does bleach also raise TA?

All hypochlorite sources of chlorine (bleach, chlorinating liquid, Cal-Hypo, lithium hypochlorite) will raise the pH upon addition, but as the chlorine gets used up and the FC level drops back down the pH will drop as well so these sources are close to pH neutral. There is some excess lye in bleach and chlorinating liquid that varies by brand and this will raise the pH over time, but usually not by very much though in commercial/public pools with high bather load this can be seen as a rise in TA over time when using carbon dioxide injection for pH control.

When the pH rises by these sources, the TA rises a little as well, but usually not measurable. The TA drops back down when the pH drops. For example, 10 gallons of 6% bleach in 25,000 gallons with the TA at 120 ppm would raise the pH from 7.2 to 7.9 and the TA from 120 to 138. When the FC level drops back to where it started, the pH and TA return almost completely to where they started. You may find the pH doesn't drop all the way down because carbon dioxide outgassing will keep it up somewhat.

 

[PaulR]

I would recommend not fussing with TA when you have elevated FC levels. The pH tests will be thrown off at high chlorine levels (> 10).
--paulr

 

[Rasalon]

I would recommend not fussing with TA when you have elevated FC levels. The pH tests will be thrown off at high chlorine levels (> 10).
--paulr

Yeah, I have already given up in TA for the moment as I tend to only focus on one thing at a time.

My FC has held, and very well, so the 28ppm shock seems to have done it. But the question is, what do I do about the high FC chlorine level now? Is it a concern, or do I just turn off the SWG and let it go down on its own? Thanks!

 

[PaulR]

Yes, turn off the SWG and let it go down on its own.
--paulr

P.S. The username just set off a ping... a fan of The Doctor, perhaps?

 

[Rasalon]

P.S. The username just set off a ping... a fan of The Doctor, perhaps?

Yes, for a very, very long time, though I still believe it has all gone downhill since Tom Baker.