FC loss, but CC is zero

[alphadog]

My season started off great (of course pool water was cool) - as things heated up I started to see a little cloudiness.

I have 9 year old gunite/plaster pool. All chemicals balanced when opened in may - CYA 50, PH 7.6 - I don't have TA or CH handy but they were all good. I just replaced my T-15 cell (9 years old) with Blueworks t-15 equivalent (24+V 6+A) as I have turned the old one up year after year, and figured it was time. But I am still seeing large chlorine drop overnight.

The FAS DPD test shows no combined chlorine - should i still SLAM? I always thought the there would be CC as an indicator if I needed to SLAM. The new SWG is not keeping up set to 75% for 12 hours. I dumped in 2 gallons of 12% chlorine yesterday AM, and brought level up to about 15ppm, this AM below 7ppm.

Thanks for suggestions - only other odd thing I noticed this year is my PH is staying relatively constant (even with new SWG cell). Past years i was adding acid all the time. I have SLAMed in the past, so familiar with process. I guess SLAM is my only option until FC Loss overnight is close to 0.

22K gallon pool, cartridge filters (cleaned pre-season) ,

 

[Katodude]

If you are failing an OCLT then yes your should SLAM. If the pool is clear, then it should go quickly. CC is one indicator, but not the primary indicator. If you see algae or fail an OCLT then you have algae.

 

[alphadog]

Thanks for the reply. I always think I have things dialed in for the year, than bam, something changes.

 

[RHanna]

I would go ahead and slam, if you think the water is looking cloudy and you are losing chlorine that much over night. I'd rather jump on it now than wait for it to get worse.

Are you measuring the FC after the sun goes down and then in the morning? Is your SWG running during this time period?

 

[alphadog]

I have not been diligent at measuring chlorine - I had some cloudiness start when the season went from cool to warm - I thought I caught it. I had never measured CC in the past, but I got an upgraded FAS DPD kit with CC measure - seeing it at zero had me looking for "other problems" instead of just SLAMing and being done with it.

Also, because I replaced my SWG cell - it is 9 years old - I was also trying to make sure the new one (as it is after market) is not a problem.

Anyway, I know the process. I think i was just in denial.