Need help, high CYA and Algae

Mitch Rapp

New member
May 14, 2016
Missouri City/TX
23,000 gallon Chlorine pool.

Our pool is 2 years old and our algae problem has gotten worse with each year. We're tired of the Leslie's circular advice and ready to go to liquid bleach and the TFP way.

1. First, our CYA is 100, which is what is probably causing our chlorine to be ineffective thus not killing the algae. It seems like the best way to lower this is to drain the pool half way. How do we do this?

2. Once drained half way, is there anything special we must do (like start up chemicals for a new pool) or do we just refill? I'm assuming once we drain the pool half way that a good brushing is required before adding water again.

3. Assuming the drain lowers our CYA to acceptable levels, what's next? Again, we would like to transition from buying the Leslie's chlorine tabs, etc. and go to liquid bleach.

I've read many of the articles in the help section and researched many old posts. I do have a general idea of what to do, but there is so much information that I'm feeling a bit overwhelmed. I would appreciate it if someone can help step by step. Thank you very much.

23,000 gallon in ground, chlorine, Diamond Brite plaster, Pentair Intelliflow Variable speed pump.
Last edited:


Mod Squad
TFP Expert
LifeTime Supporter
Apr 17, 2010
East Texas
A CYA of 50 in Texas will be fine. You can rent a submersible pump or buy a cheapie from harbor Freight. Refill, ....TEST..........balance. Got one of our recommended test kits? Welcome to the forum.


Well-known member
Apr 20, 2017
How do you know your CYA is 100? Did you test it yourself with one of the recommended test kits on here? I'm asking because the pool store is extremely inaccurate on testing CYA.

Also, if you tested yourself you need to do the dulution CYA test to make sure it's not even more than a 100.
May 14, 2016
Missouri City/TX
Thank you everyone.
1. I have not gotten the test kit yet. I've been using an old Taylor test kit and the pool store tests.

2. BTW, does anyone know how long the test kits last? My buddy had it sitting in his garage for two years when he gave it to me. Do the testing chemicals deteriorate over time?

3. Any recommendations on the best place to buy a test kit?

Thanks again everyone.


TFP Expert
LifeTime Supporter
Jan 6, 2010
San Dimas, CA (LA County)
Welcome! :wave:

Sadly, your scenario is probably the most common on this forum.

I'll pile on and say
1) order a proper test kit. My advice is the TF100 with the XL option. You'll be burning through a lot of the FAS-DPD reagents and you won't find them in stock at a pool store so you might as well get the refills now.
2) Drain off a little more than half. The CYA tester stops at 100, and the graduations aren't equidistant, so what might look like 110 or 120 is more likely something closer to 150. Tip: if the pool store lists it as 99, that's code for off the scale. Second tip: If there's any sludge buildup on the floor, brush it towards the pump and maybe it will get sucked out so your filter won't have to deal with it later.
3) Refill and let water circulate to mix. Brush a bunch to help mix it.
4) Test. Then post results and we can advise you on the next step.