So I have been battling with disappearing chlorine. I have an automatic chlorinator using 3inch tabs and have it set to 5 which is the highest setting. Tested my water last weekend and the FC was 0.5. Figured I would shock it so did that and the next day FC was at 5.5. A couple days later I was back at 0.5 and also noticed I had a few uninvited swimmers (water boatmen and / or back swimmers). This indicated that I had algae although there is no visible sign anywhere. I shocked the pool again and of course FC came back up.
We have had a few good days of bright sun and the pool sits in full sun pretty much the whole day. We have also had a LOT of rain recently so that too is playing havoc.
This morning I ran my tests again and these are my numbers:
pH = 7.6
FC = 0.5
CC = 0.0
CH = 250
CYA = 60
Looks like everything is about where it should be with the exception of the FC. Also noticed I again have one or two of those uninvited swimmers (when I see these I skim them out and dispose accordingly)
So I am planning to SLAM the pool. Looking at the Chlorine / CYA Chart, looks like with a CYA of 60 I need to target an FC level of 24. Using pool math with my pool of 19600 gallons I need to add 957oz of 6% bleach to get to FC 24
I plan on using Walmart bleach (trip to Walmart coming up shortly). I will add the 957oz and then plan to test the FC every 30 minutes to 1 hour for the first few hours until I see FC loss slowing down at least.
1. Does my reasoning and approach look reasonable? Any errors or omissions in my methodology (I plan on turning off my automatic chlorinator during the SLAM process)
2. It is currently raining very heavily here and there is a lot of rain forecast over the next few days. With all this rain I may not be able to SLAM it till next weekend. Should I put in a few gallons of bleach anyway just to try and bring the FC level up and keep adding it as needed over the next few days / week or is this a fruitless exercise. My thinking is some FC would be better than none, but is it just pouring money down the drain?
Thanks for all input and assistance - I have never SLAMed my pool before so want to be sure I am getting it right