Trouble Getting The Right Balance

[bluenoise]

Hello, everyone-

I stumbled across this great site in a Google search and I'm glad to have been lurking for the past several weeks. I finally have a question of my own.

I have a 20,000 gallon in-ground plaster/gunite pool that is solar heated. We keep it around 87 degrees in the summer. This year, I'm having a difficult time keeping it chlorinated and I've had a couple mild blooms of algae and a little "pink algae," which I understand is not actually an algae.

The guys at the pool store sold me an anti-algae product that I used to kill the algae, but it really jacked up my pH and TA. After using this stuff ("Green to Clean," I think), my pH and TA were both really high. Using muriatic acid, I managed to get the pH down to 6.8 and the TA down to 170. After reading here about lowering TA using muriatic acid and raising pH using aeration, I've been trying that for the past few weeks. I got the pH down to 6.8-7.0 and it's not gone anywhere since I last added acid about three weeks ago. The TA is now about 150, but I don't want to add any more acid until I get the pH back up a touch. To aerate, I turned the returns upward such that they ripple the water's surface. Also, the solar is sucking in air via its relief valve, so there are lots of bubbles in the return water. For some reason, though, the pH is not moving nor is the TA. Both are holding steady for the past ~10 days.

My chlorine is going fast, too. I have several three-inch tablets in a floating chlorinator and I have to add at least two tablets a week and it's still not keeping up. I have been tossing in about two to four cups of Chlor-Brite every four days and it's still barely keeping my chlorine levels in the "ideal" range. Is this because my TA is so high? I still get a little algae (green), too. I've been running the filter pump at least 12 hours a day, the cartridge filter is clean, and the Polaris 360 goes for about two hours a day, too. A week ago, I tried shocking the pool by adding 12 cups of Chlor-Brite and then running the pump for 24 hours. At the end of the 24 hours (the next morning), there was barely any chlorine in the water.

We're planning on installing a salt system soon, but I feel I need to get everything into balance first anyway. The water looks fantastic, but it's very close to getting another algae bloom.

In the past few years, I've never had the problems I'm having this year with the high TA and the rapid use of chlorine. What's different this year?

[waterbear]

Please post a full set of test results for FC, TC, CC, pH, TA, CH, and CYA. I suspect that you have elevated CYA levels from the trichlor and do not have enough FC in the water to prevent algae because of this.

[bluenoise]

Please post a full set of test results for FC, TC, CC, pH, TA, CH, and CYA. I suspect that you have elevated CYA levels from the trichlor and do not have enough FC in the water to prevent algae because of this.

Unfortunately, my test kit doesn't test for CH or CYA, so the reset of my results may be moot:

FC = 3 (at least for the day after I blast it)

CC = 0

pH = 7.2

TA = 150

This is according to my "DPD Deluxe" test kit from Leslie's: Link to test kit

I suspect you're correct about me not maintaining enough FC to keep algae at bay as I'm having a lot of difficulty keeping it elevated. It's going really fast, which is one of the reasons for my questions. Namely, why am I blowing through chlorine so quickly?

[waterbear]

If you have algae it will consume chlorine very quickly. Also, certain types of algaecides (chlorine enhancers based on sodium bromide or inorganic ammonia) will also create a very big chlorine demand and make it difficult to maintan a FC level after their use. Get your water tested and post a full set of results.

[bluenoise]

If you have algae it will consume chlorine very quickly. Also, certain types of algaecides (chlorine enhancers based on sodium bromide or inorganic ammonia) will also create a very big chlorine demand and make it difficult to maintan a FC level after their use. Get your water tested and post a full set of results.

So, here are the results from this morning's test:

FC = 2

CC = 0

pH = 7.2

TA = 150

CYA >150*

* I haven't had the time to get the CYA tested by the store or with a proper test kit, but my test strip test showed it north of 150, which seems to confirm some suspicions posted earlier in this thread.

So, as I understand it, the only way to lower the CYA is to do a partial drain. I'm guessing I'd need to replace about half of my water, right?

I'm installing a SWG in the next week or two, so it would make sense to do the water replacement before I add the salt. However, we're planning on resurfacing the pool this fall, so it might make sense to live with the high CYA until the pool needs draining anyway. Of course, I'd need to re-add the salt after that, but that cost seems minimal in the grand scheme of it all.

Does anyone have any thoughts on this plan? Would leaving the CYA that high for the rest of the swim season mean I won't be able to keep up with the chlorine demand with my SWG? I've ordered the Aquarite generator, which claims to be able to support a pool twice the size of mine.

[waterbear]

Goldline controls recommends a CYA level of 60-80 ppm and I have found that 70-80 works very well. Get your CYA down to that level (and DON'T use strips to do it...they are just not reliable!)

[bluenoise]

Goldline controls recommends a CYA level of 60-80 ppm and I have found that 70-80 works very well. Get your CYA down to that level (and DON'T use strips to do it...they are just not reliable!)

What bad things might I expect if I try leaving the CYA at its higher value for the remainder of the swim season? Can the Aquarite keep enough FC in the water to offset that CYA? As I understand it, I'd need to keep the FC around 11-12% of the CYA, so that'd be around 18 ppm. As I mentioned above, I'd like to avoid draining my pool twice this year, but I will if necessary.

[waterbear]

One of the main problems you will encounter is that your pH will rise very fast since you will need to operate the SWG at a very high output to produce that level of chlorine. Bite the bullet and start drains and refills. It's for the best.

[bluenoise]

One of the main problems you will encounter is that your pH will rise very fast since you will need to operate the SWG at a very high output to produce that level of chlorine. Bite the bullet and start drains and refills. It's for the best.

Bummer. So, would it be better to drain off a bunch of water at once or do it more slowly (ie drain off about 12 inches, refill it, repeat)? It seems like it would be less wasteful to do it all at once as then I wouldn't be draining any of the refill water. However, should I worry about exposing too much plaster or reducing the weight of the pool against potential hydrostatic pressure? We have clay soil (rock hard) and it's very dry, if that matters.

How much should I replace, assuming my pool is 20,000 gallons and the CYA is in the neighborhood of 150? I don't know if the replacement tap water has any CYA in it.

Thanks for all your help and advice so far. That goes for all the other experts here, too, as I've learned a ton from this forum since I first found it.

[waterbear]

Your tap water should not have any CYA in it. If it does then I would contact your water company since that would mean your water is contaminated (probably with runoff from herbacides, which degrade to CYA and other things from bacterial degredation).

It is usually safe to drain to a foot or two below the skimmer but if you can safely drain more then that would be a faster way to reduce the level. You are looking at replacing about 50% of the water in your pool. Then again, it's hard to measure CYA levels above 100 ppm so your actual level might be higher. The strips are just not that precise. Also, if you have had high CYA levels for a while it is possible that some might have deposited in the surface of the pool and in the plumbing and as you lower the level it will redissolve so you might have to do a second water replacement in a week or two after you initially get it to where you want it.

[bluenoise]

Your tap water should not have any CYA in it. If it does then I would contact your water company since that would mean your water is contaminated (probably with runoff from herbacides, which degrade to CYA and other things from bacterial degredation).

It is usually safe to drain to a foot or two below the skimmer but if you can safely drain more then that would be a faster way to reduce the level. You are looking at replacing about 50% of the water in your pool. Then again, it's hard to measure CYA levels above 100 ppm so your actual level might be higher. The strips are just not that precise. Also, if you have had high CYA levels for a while it is possible that some might have deposited in the surface of the pool and in the plumbing and as you lower the level it will redissolve so you might have to do a second water replacement in a week or two after you initially get it to where you want it.

I just ordered a good test kit today, so I should be able to get some true readings in a week or so. In the meantime, I've been trying to hold the chlorine up north of 33 ppm (based on volume calculations, not measurements) for a couple of days before I let it settle back down to around 12-15 ppm over the weekend. I will be gone all weekend starting tomorrow, so I'm going to give it another blast of bleach tonight.