What in the CYA???


New member
Apr 29, 2016
San Antonio Texas
Hi all,

Please bear with me...

I have been an inground pool owner for about a year now. It's been a tough year moving from north to south and then also trying to get a grip on owning a pool. I have been working at taking care of my pool 100% on my own, but have had issue, upon issue and just waiting to get through our worst season before taking the leap.

I inherited a 20 year old sand filter and a residence where the owner liked to cut corners. We had the hail storm of the century last year that turned the pool into a swamp. After clean up was done the pool was diagnosed with high CYA and we did a partial drain. And of course.. it condinuted to repeat. I hired a different company who drained the pool and we started from scratch. The pool has continued to struggle with algae. Finally in January I decided to install a new DE filter and new VS pump. The company also emptied the pool and acid washed the plaster at this time. Such a difference! But still, as the weather warmed, the sides and bottom of pool started greening up...and it is evident where the plaster was sprayed with pressure washer and where it wasn't. The company that has been tending the pool uses dichlor. As I didn't want the CYA to creep up again.. I decided to manage the chlorine myself with liquid chlorine 12% and start the process of weaning away from the company while keeping a safety net in place to get me through the worst season for pollen, leaves debris and torrential rain.

I found granules in the pool sweep tonight after the tech had been here. I called and asked what had been added and he said shock and that I should not to use anything with conditioner because the CYA was elevated to 80 again. I informed him that I had only been adding liquid chlorine since the new pump/filter was installed.

So... my main question is this... is there any way that CYA increases without it being added? Any condition in the plaster etc., that would account for this? Just mind boggling that it's creeping up and I am using only liquid chlorine 12%. The pool was pretty stable until live oak fall late Feb, then pollen tassels most of March and now thunderstorm season. And yes.. the pool is slurping up chlorine at this point. I believe will improve once there is less going into it from Mother Nature.

Feel free to talk about the algae too.

I have a FAS-DPD arriving tomorrow :) and have plans to SLAM the pool (per instructions on this site) as soon as weather clears or perhaps even while it's coming down.

I am just perplexed by the CYA that is climbing without being added... and the algae that never dies...

Thanks for your patience.. I know this is not the usual format. Just don't know where to start.

Seriously, thanks.



Well-known member
Aug 14, 2013
Fayetteville, NY
CYA does not climb without being added. However, it is difficult to measure accurately, so it may appear fluctuate, even with a good test kit.

You are on the right track getting a high quality test kit, and planning for a SLAM.

Sent from my MotoG3 using Tapatalk


Aug 4, 2016
ellisville, MO
Hello Kristi,

Welcome. I am also a new pool owner, going on my second summer. You can check my tribulations last year with this post About Time

But to answer your questions. My understanding is that dichlor, powder shocks, and any other non liquid chlorinators will have cya. Also cya take time to go into solution so it could appear to creep over a few days.

The trick I found to cya testing was serial dilution and starting with a cya >300 it was necessary to learn this little trick. Also a DPD test kit is the only way to go. Good luck and ditch the dry.


Bronze Supporter
Dec 22, 2016
Arlington, Texas
Agree on the testing yourself, however, dichlor does add cya. Every 10 ppm FC addition through dichlor adds 9 ppm CYA. Ditch pool service companies all together. They are just taking your money and jacking up your pool's chemistry

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