I thought things were going well but....

[Philo]

The pool water looked perfect until we had several swimmers for a few hours. Then, cloudy.
The FC has never ever been below 6 ppm.

What happened?

FC 10
CC.5
pH 7.6
CYA 70

 

[lightmaster]

Have you cleaned your filter recently?

 

[PAGirl]

If the swimmers were wearing a lot of sunscreen it might cause issues.

 

[Philo]

It's a little more clear today. Filter is clean don't know about the sunscreen used.

Something doesn't seem right.

 

[lightmaster]

Do an OCLT tonight and see if you geta FC loss of more than 1ppm. Raise your FC to above 10 after the sun goes down and test half an hour later, then test again BEFORE the sun comes up

 

[Philo]

Just curious, why raise it above 10?

Thanks

 

[lightmaster]

From what I've read on here, a higher level makes it easier to see any changes in your FC. I'm not sure on the exact reason, but I've read a lot of the "TFP Experts" saying to bring it up to 10 for an OCLT:

Any tips before this newb tries to do an OCLT
OCLT question

 

[domct203]

Over time we have found that there is really no need to raise (or lower) your FC level for the OCLT. As long as it is at least 3ppm is fine.

From step 2 of the OCLT:
"After the sun goes down, and at least 30 minutes after your last chemical addition of the day, test your water for FC using the FAS-DPD test making sure your FC level is at least above 3ppm."

With our lowest CYA recommendation of 30ppm, the FC should be in the target range of 4-6ppm anyway, and is fine for an OCLT.

Seeing that the OCLT is usually ran during a SLAM, FC will usually be above 10ppm, and I believe that is how the "above 10ppm" got started.

No harm either way.