Passed OCULT once, next time - nope!

[Jkpharm]

Two nights ago, we did an OCULT and passed. Whew! I thought we had turned around. Last night we did a re-trial just to make sure. Nope. We lost 1.2ppm FC and CC is at 1. Is this normal?

I did a re-trial because I wanted to make sure we were in the clear before putting the solar cover back on at night time. I need to rule out that there isn't something on the cover causing us to lose significant amounts of chlorine over night.

 

[Texas Splash]

You did the right thing! Your gut told you something wasn't right, and it's good you double-checked. Having said that, let's review the SLAM requirements:
The following 3 objectives must be met:
1. Water is clear
2. You do not lose any more than 1ppm of FC overnight (that's the OCLT)
3. CC (Combined Chlorine) is <.5
** You MUST meet ALL 3 items above to properly do a SLAM. Simply “spiking" the FC higher than normal isn't SLAMming, therefore there’s a good chance your algae will return.

Now if you have a concern about the cover somehow contributing the your OCLT, I supposed you could just leave it off for a night and do an OCLT the next morning. If it passes, put the cover on and try again the next morning to compare. Otherwise, it may simply be that you still have a small amount of residual matter in the water that is trying to fight the bleach. Stay with it!

 

[Bama Rambler]

I always suggest that people run the OCLT two nights in a row just to make sure that the first one wasn't a fluke. It's not part of the process, and most of the time one night is enough, but there are a few times where someone will pass the OCLT and not be completely done SLAMing.

I'd bring it back to slam level for a couple of days and then run it again. You can also put the solar cover on it one day during slam to kill anything that may be on it.

 

[ping]

removed post

 

[Isaac-1]

Double check for places with poor circulation where algae may be hiding, under steps, behind light niches, etc.