Where's the chlorine going?

topherchris

Member
Jun 2, 2019
9
Cleveland, OH
First full year managing our pool. I opened my pool on 6/1. It was a bit cloudy, but cleared up in 1 day with shocking and vacuuming. I backwashed the filter after vacuuming.. The pool has been crystal clear since then and the CC has been <0.5. I forgot about the OCLT in the excitement of clear water! Afterwards, I noticed that my Chlorine requirement seemed high. I was adding about 2 quarts of 12.5% chlorine daily (16,000 gallon pool with little sunlight exposure). I performed an OCLT and had a drop of ~4 ppm, so I started the SLAM process over again on 6/10. I've been keeping the FC ~20 and testing several times per day, but still keep failing the OCLT. Last night if dropped 5 ppm in ~ 9 hours. The pool has been covered by an autocover almost 24/7, so the loss from sunlight should be almost nothing. That leaves consumption by organics, but I'm not sure where they could be. I've scrubbed every inch of the pool. I don't have any removable ladders. I've backwashed the filter. The only place I can think of that I can't visually examine is the bottom of the autocover. Has anyone else had issues with algae on the bottom of the autocover? In retrospect, I started managing the pool last August and was using triclor tabs (using BBB method now). Even then, I had trouble keeping the FC level up although I never had an algae problem.

1.) Should i be concerned about the algae on the bottom of the autocover?
2.) Am I just being impatient after 2 days of SLAMing? I assume I should just keep at it? How long can I expect it to take?
3.) Any other sources of organic material I'm not considering?
 

mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
20,233
Laughlin, NV
Two days would be nearly a world record for the shortest SLAM -- so stay at it.
I would suggest you open the cover for most of the day to ensure you burn off the CC's in your water.
If there is algae on the bottom of the autocover that is a concern. It needs to be fully bathed in the SLAM level water.
Do you have a light? If the kind you can take out, do that as algae can hide in the light niche.
 

topherchris

Member
Jun 2, 2019
9
Cleveland, OH
Thanks for the reply. Do we have to wait until the SLAM is completed to swim in it? If I let the FC level drift down overnight to below SLAM level during the day, is it OK to swim or should I just keep the FC above SLAM level 24/7?
 

mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
20,233
Laughlin, NV
Water temperature has minimal effect of FC consumption.
You can safely swim in a pool as long as the FC is above the minimum and at or below SLAM level based on your CYA. You must also be able to see the bottom of the pool in the deep end of the pool.
 

Richard320

TFP Expert
LifeTime Supporter
Jan 6, 2010
22,052
San Dimas, CA (LA County)
I'd look behind the light and beneath the autocover. And do you have an autofill? Check this out. For that matter, inside the pump basket and inside the filter are also part of the same body of water, whether you can see it or not. What if you sucked a mouse or a frog in?
 

topherchris

Member
Jun 2, 2019
9
Cleveland, OH
I'd look behind the light and beneath the autocover. And do you have an autofill? Check this out. For that matter, inside the pump basket and inside the filter are also part of the same body of water, whether you can see it or not. What if you sucked a mouse or a frog in?
That is really gross. No autofill for me. Nothing beside the usual plant matter in the skimmer and filter baskets. I check them pretty frequently. Maybe I'll take apart the filter instead of just backwashing it. I did open it up before I opened the pool and it was clean. Thanks.