CYA to FC Correlation

johnsonatx · May 14, 2017

Currently my CYA is 50 and I've been pouring about 64oz of 12.5% bleach in daily to keep FC at 6 (14,500 gallon concrete pool). It seems a lot to me but maybe I'm just not used think liquid chlorine stuff as I just switched off pucks a couple weeks ago. All my other chemistry numbers are in check and water is crystal clear. When I have been checking every morning I am getting FC reading of only 1 which means I am losing 5ppm every day. That seem plausible? I would like to only be adding every other day as every day is kinda of a PIA, the pucks did have that going for them. Also with high CYA will the FC still show up on test even though it's not being used because of so much stabilizer of does the high CYA cancel out those FC readings?

Thanks for your help

pabeader · May 14, 2017

Does the pool get sun most of the day? Have you tried doing an OCLT?

Jimrahbe · May 14, 2017

J,

We usually say that pool uses 2 to 4 ppm of chlorine per day. Your 64 oz of 12.5% chlorine adds 4.3 ppm to your pool, so you are on the high end..

As Bob suggests, I'd do an OCLT just to be sure it is the sun and not something in the water eating your chlorine..

What you are finding out is exactly why a lot to TFPers are using a Stenner pump system or Saltwater Chlorine Generators...

Thanks for posting,

Jim R.

johnsonatx · May 14, 2017

Thanks I will try the OCLT this evening, and yes I've been looking at the Steener pumps and automating this process. If I had algae or something else in the pool wouldn't I see it? The water is crystal clear and no complaints minus the excessive chlorine I appear to be using

jblizzle · May 14, 2017

It is possible to have algae that you can't see yet.

johnsonatx · May 14, 2017

It does get a fair amount of sun throughout the hottest part of the day, and I'm in Austin too so it's hot

Richard320 · May 15, 2017

Besides running an OCLT, here's a few other things to consider
1) Testing error on the CYA. If you didn't have bright light, the dot will disappear too soon and give you a falsely high reading. I can see a distinct difference in results if I hold the view tube at just the top with thumb and forefinger or if I hold it more naturally with all my fingers touching.
2) The pool is bigger than you think. When you dose with acid or bleach, do you see the results you're expecting or come up short?
3) The bleach is old and not full strength anymore. If you get it at a pool store, there's probably a quick turnover. If it came from Lowes or Home Depot, it could have sat out in the garden center over the winter. Check the date code on the box. https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=0ahUKEwjX88jBifLTAhVC7GMKHd2pCgkQFggjMAA&url=https%3A%2F%2Fwww.troublefreepool.com%2Fthreads%2F83147-Chlorine-Date-Code-Decoder-Easy-Way-to-Measure-Strength&usg=AFQjCNEZXCJrWRX5g51X_QDXO-lmXZ6zMg&sig2=aH284ShwM3b8XH92eqK-5Q

johnsonatx · May 26, 2017

Must of had something in the pool that I couldn't see even though water was crystal clear. I went ahead and slammed it. Took FC up to 20, and after it settled back down to norm I appear to be doing a daily burn of 3ppm. So dropping from 6 to 3 FC per day and dropped my liquid usage from 64oz a day to 44oz. Think I'm good to go now.