Hailing from Florida


May 21, 2017
St. Leo, FL
Treating pool with high CYA

2017_05 Pool Log.jpg

I had a bunch of background information that I lost when the site logged me out while I was creating this post. After I logged back in, my edit was empty :-( One more time....... (there is also history in the Introduce Yourself - Hailing from Florida)

Have had house since late April. Empty for 1 year, bank owned, no idea if pool was maintained by previous owner, but I don't think so. Bank dropped 3 tablets in pool, and set auto-chlorinator on max 5, but the filter was not running and water level was 8" low when we bought it. Bottom line, I have no idea when the last time was for quality water. The water was NOT green when we moved in.

As you can see above, I am dealing with a high CYA issue. The 105 reading was the pool store, and I doubt it is accurate. My TF-100 kit arrived on 05/24, so all readings after that date are with the TF-100 kit.

I believe I am still dealing with some algae. I do not have an auto-cleaner, and if I go 3 days without vacuuming, when I do start brushing the pool sides, I raise a "little cloud of dust" in some spots. The water is really clear other than that. Do I need to be vacuuming every day if the pool water quality is correct? Pool is in a screen enclosure, so almost no debris gets into it.

(CYA and FC tests are done with 1:2 dilution, to keep from consuming my kits)

Due to the high CYA, I believe I have to keep my FC up around 18-20 to be safe. While I was waiting for the test kit, I dumped in 3 gals of 6% bleach to hold the algae at bay. When the kit arrived on 5/24, it showed my FC was at 33. The next morning it was still at 33, and CC of 1 looked okay. Not great or good, but okay. So I interpret that to say I (algae) am not consuming much FC at night. Yesterday, I lost 5ppm during the day, assuming mostly due to sunshine, although I would have thought the high CYA count would diminish the effects of the sun??? As you can see, that FC held through the night, and my CC was an even better .5ppm this morning. Looking real good!
Then I brushed the pool and noticed I was still stirring up a few minor "dust clouds". Knowing that algae is binary, you either gots it- or ya don't, I decide to take my pool up to slam level. But what FC level would I need for CYA of 140?

I have the spa drain cracked open, and the spa return adjusted so I am just barely spilling water into the main pool, while the main pool drain is fully open, and all pool returns are at 100%. This I believe is giving me the most thorough circulation I can get in both spa and pool)Using PoolMath, I plug in my FC of 28, and a goal of 60. It tells me 663 oz of 8.25% bleach. I dump 256 oz into the pool and spa areas and gave it about 1.5 hours before I tested. FC was 54. But that was only about 40% of the amount??? So, I'm guessing it may not have circulated quite enough. 4 hours later I test, and FC is at 49. Okay, makes sense to me. I was probably not fully circulated before, and of course, the sun has been nibbling away at my FC all day as well. My CC is 0, and has been there for 2 days now, which I "think", is telling me the chlorine is not having to work at killing anything. Do I have that correct? I also have NO odor at all by the pool, and the water looks especially clear. I can still see some very small brownish colored flakes on the pool surface, and if I gently skim with the net, I will collect quite a bit of this 'stuff'. Looks like junior scum that just hasn't had time to brew yet.

Need advice at this point. Should I take it up to 60, or higher, to ensure if there is any algae that I have it killed off? Or does the CC=0 reading already tell me that, and I should let the FC level fall to 18, and then do a full strength test of FC and CC?
How can I test pH? If I let FC get to 10, isn't that too low for my CYA, and would I be at risk for trouble?

I will get a better photo of the pool and water later. Too many shadows being cast onto the water right now.
Last edited:


Gold Supporter
May 19, 2016
Re: Treating pool with high CYA

Hi Gordy - I'm sure a moderator will chime in soon, but with a CYA that high, I'm 99% certain the first step most will recommend is a partial drain and refill to get your CYA down. The CYA test cylinder isn't graduated evenly, so there's no way to tell if it's 100, 140, 200, or even higher. And trying to maintain a TFP pool with that high of a CYA isn't going to be reasonable, to my knowledge.


May 21, 2017
St. Leo, FL
Re: Treating pool with high CYA

Thanks for responding. I know it is not ideal, but our county is under severe water restrictions, so dumping is not an option, until maybe fall. Even people on wells are not permitted to 'waste' water. Best I have been doing is draining off a bit of water when rain is in forecast, hoping to take CYA down .001 at a time. 100,000 rainfalls will help my cause.
I got the CYA by diluting the test water in half, which then gave me a reading of 70, which gets doubled to 140. Found that technique in some older posts.


Well-known member
Mar 26, 2014
San Jose, CA
Re: Treating pool with high CYA

I doubt you'll be at any risk of getting algae if you let the FC drop under 10. Just make sure you brush the walls and the floor while you're letting it drop. Take your pH reading and then raise the FC back up to a safer level. If you do it quickly, you should be fine.

Your water looks crystal clear, so I doubt you need to keep slamming.


Gold Supporter
May 9, 2017
Central, OK
Re: Treating pool with high CYA

For a CYA level of 140, the absolute minimum FC level, i.e. the level it should never drop below, is 10.5 ppm. The bottom of the recommended range is 16.1 ppm.

It's really not feasible to maintain a pool at this level for long. If you were to have an algae bloom, your SLAM level would be 56 ppm which equals $$$!

I think it's good advice to do a 50-60% drain and refill as soon as is feasible.

Good luck