TA high, pH low, where did my chlorine go?

[compuboks]

I humbly apologize if any of this is repeated in another thread. I've been combing through here for the last several hours trying to figure out what I need to do and still don't have a definitive solution.

Background: Have a 35,000gal gunite/plaster private pool. Serves 60 condos, usage varies from 5-20 users/day Summer to 10-40 Winter (Big old 102F hot tub in the winter - Ski Resort amenity). Summer is the relevant season right now.

I've been maintaining this pool for about four years now. I'd had no water balance issues until last fall when we did a full drain/refill from city water. Last winter start I had some low pH issues which had NEVER been a problem before (usually only high pH problems). I corrected with soda ash and didn't worry about much beyond that. THIS spring startup, I've been battling everything. My pH has been consistently too low (started at 7.0), my TA is high (started at 180), and no matter how much trichlor (my only sanitizer) I add I'm only seeing 0.5 to 1.0ppm FC on my test kit.

Now, I did do several things differently this year. Between seasons, instead of keeping a small number of trichlor tabs in the my injector I left it empty and the pool covered for two months - Basically just circulating unheated with no treatment. Because of this I had a bit of a green algae bloom. I corrected with a granular chlorine shock (the type escapes me right now, pretty sure it wasn't trichlor). Since however I haven't been able to control the chemistry.

I started by trying to correct my low pH with soda ash (per kit instructions), which obviously upped my TA a bit (220 at the highest) but got my pH under control to 7.4-7.6 ish, but still having low chlorine problems. I was then advised by someone I work with who did pool work back in the day that I should first get my TA in line before I start troubleshooting other problems. He told me to shut all system circulation down and add acid slowly in the deep end, brush, then wait two hours before restarting the system. He said It should adjust the TA and leave the pH alone.

Well, I added a gallon of muriatic acid and the TA number did go down 10ppm (to 150 from 160), but my pH also dropped to 7.0 again - which was what I figured would happen in spite of my elder's instructions. I re-adjusted pH with soda ash again, and also airated the water - The pool has a pretty high powered jet/bubbler system system in the shallow end for winter use. FC is still low, not testing TA until tomorrow to allow the pool to be filtered.

I'm using a Taylor test kit. It does Chlorine, pH and TA. It does not do CYA, but I've been using a test strip kit (which I gather noone here likes) as a comparative test method. It shows stabilizer at 0-50. I've read this may by the same thing as CYA? Which perhaps could also be a factor here?

I'm obviously lost here. The one thing I've learned from reading this forum so far is that maintaining a pool can be vastly more complicated than a skim, vacuum, and chlorine tablet here and there to fix the world's woes.

[chem geek]

The test strip is useless, especially for CYA. The Taylor K-2006 kit has everything you need including a CYA test and an accurate FAS-DPD test. Or you can just get a CYA Test and FAS-DPD Test separately.

For every 10 ppm Free Chlorine (FC) added by Trichlor, it also increases Cyanuric Acid (CYA) by 6 ppm. Your CYA may very well higher than the test strips indicate. That causes the active chlorine level to be lower. If you insist on using Trichlor and your CYA gets high, then if you don't proportionately raise the FC to be at least 7.5% of the CYA level then algae can grow faster than chlorine can kill it. In that case to prevent algae growth you can use an algaecide such as Polyquat 60 weekly or you can use a phosphate remover.

I suggest you test your CYA level. If you want to lower the CYA level you have to do a partial drain/refill to dilute it.

See Reduce Alkalinity Levels for the proper procedure to lower TA if that's what you want to do. Trichlor is acidic so needs a higher TA to balance the pH, but this balance will depend on the amount of aeration (splashing) in the pool which is why it may vary from before.

Learn more about how to manage the pool by reading the Pool School. You may want to consider getting a saltwater chlorine generator or using sodium hypochlorite with a peristaltic pump, or at least to shock with chlorinating liquid to reduce your dependency on Trichlor.

[compuboks]

Thanks for the reply. I ordered a full K-2006 kit today at my pool supplier. They didn't have any single CYA tests in stock (said they practically never use them) so I'll have to wait for my new kit to find out where I'm at.

I'm not married to using Trichlor only, if there's a more balanced approach I'm open to it - It's pretty much what I inherited and was trained to do. Our pool can go through a fair bit of sanitizer volume though. We get a reasonable amount of use and we're at high altitude (6000ft - Right at the base of a ski hill, great view!). The pool is always uncovered in the summer and gets a lot of sunlight. My local supplier tends to be limited in what they offer sanitation wise - Really just Trichlor and Bromine tabs, and several flavors of granular. I added some granular Cal-Hypo today to try to boost my FC a bit. Got it up to 1.0FC at the end of the day and put four more tabs of Trichlor in for the weekend (I know - may be adding to my problem). You mentioned that Trichlor does have issues controlling algae, and we have had an ongoing black algae problem in the hard corners and plaster imperfections in the pool over the years.

After my adjustments yesterday I'm sitting at pH 7.4 and TA of 200. I'm hoping the TA settles out over the weekend. If I have to adjust TA again next week I'll use the method you linked instead of what I did before. I have very good aeration options with our jet system, and if that works for raising the pH it seems like the way to go. I ended up adding a bunch (8lbs, specifically) of soda ash to correct my pH yesterday after using acid for TA. And then, big shock, my TA jumped again. I think I'm trying to do too much too fast and not the right way. I probably need to give my chemistry more time to settle between changes.

Salt chlorination is certainly an interesting option. Several pools up here have swapped in the last few years. I've taken a swim in one and thought it was great. I need to read more about it though. Seems like something hard to bite off for us right now (cost and learning curve wise).

Thanks for the Pool School link. I skimmed it a bit (pun not intended) today at work. The basics I mostly understand, I'll try to devote some time over the weekend for the more conceptual stuff I'm missing and browse this forum more. You guys are a great resource.

[chem geek]

Trichlor, per se, is not the problem. It's the CYA that Trichlor adds and builds up that is the problem, especially if you do not raise your FC proportionately with the CYA level. The fact that you have black algae proves that since it is almost unheard of in properly managed pools with a minimum FC that is 7.5% of the CYA level. Green algae is also prevented at this level.

I'd bet you'd be surprised at how many places carry chlorinating liquid that you can compare to bleach prices. Hardware and big-box stores as well as some pool stores.

[compuboks]

Update, finally got my K-2006 test kit. Here's where I stand:

FC - 0
pH - 7.3
TA - 170
CYA - 50
CH - 260

I'm thinking I simply need higher chlorine doses to start with, and the TA may be a little too high at this stage...