Is it normal for FC to increase over many hours?

jlt19

Active member
Aug 20, 2019
37
St. Louis, Missouri
I'm in the middle of a SLAM and having to maintain very high FC due to high CYA. I was at 140 for quite a few days, so targeting 55. I checked after work and FC was 51, so I added enough to bring it to 55 around 4pm. Then tested around 6pm and it was 56. Great.

But I tested again around 10pm and it was 61. Is it normal to continually go up? My pump has been on the whole time. It's around 85 degrees, but no sun on the pool the whole time. I don't know water temp, but it's not very warm.

Additionally I checked CYA 2x tonight for the first time in about a week and it dropped to 120 (rain/drain I guess). So I've been overslamming. Wonder if that's why I still don't have crystal clear water even though CC has been 0 and OCLT has been roughly 1-2 ppm lost per night.

I'll let it drift down a bit now but the slow increase over 6 hours concerned me.
 

ajw22

Gold Supporter
TFP Guide
Jul 21, 2013
9,760
Northern NJ
The variability of your testing is within normal testing error at those high levels. Your chemicals are not drifting, it is normal variance of testing.
 
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jlt19

Active member
Aug 20, 2019
37
St. Louis, Missouri
Thanks. But then that gets concerning when trying to maintain and check OCLT.....

These are my test numbers for the past few days. It was still dark outside this am to tell how it looked. I didn't add any LC though. I haven't always tested for CC.
This is all assuming I've added the proper amounts per pool math, except at 1pm on 9/7. I only added 2 cups but it should have been 2qt & 2c. Short term memory loss.
early sept chem tests.JPG
 

ajw22

Gold Supporter
TFP Guide
Jul 21, 2013
9,760
Northern NJ
These are the problems of trying to manage high CYA & FC levels.

At those high FC levels you will lose FC naturally. I can’t interpet your FC log because it doesn’t show how much and when LC was added. It would be helpful to put it all in PoolMath

What do you intend to do about your high CYA?

How does your water look?
 
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jlt19

Active member
Aug 20, 2019
37
St. Louis, Missouri
Gotcha, I did put it all in there but haven't upgraded the app yet as I planned on doing it upon spring opening. I added 12.5% in the amounts it told me to at each testing for SLAM at 140, which was 55 target FC. Until yesterday when I realized CYA dropped to 120.

Only reason I'm leaving CYA so high is because to drain now would require renting a pump and then we have to do that again to close. We'll close first week of Oct (if water temp is low enough-leaving for 8 day trip soon after).

Hoping cya will drop some over winter but if not, we'll take care of it in spring.

Water is clear now (was a green mess about 2 weeks ago). Still gets spots every day on the floor, but it's probably dirt. Lots of leaves and acorns and some other things falling constantly. Wish I had $5k to take down my oak tree...
 

mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
22,396
Laughlin, NV
Every pool owner should consider owning a small sump pump. They can be purchased via Amazon or at a Harbor Freight if you have one. Then there is no need to rent a pump. Or attempt to manage a pool with very high CYA.
 
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