25,000 gallon in ground plaster pool, variable speed pump, DE filter. Currently using manual chlorination and acid using liquid chlorine and liquid muriatic acid. Recovering from excessive use of ch tabs by former pool guy.
Location, southern California.
Before I learned enough from this site to be confident in being able to manage my pool myself and send my pool maint. company packing, they had used pucks exclusively via feeder and though I had refilled the pool 2 years earlier, my CYA had increased to 150. I got tired of algae problems and their monthly fee made me think "with all these problems what am I paying for anyway?" This website helped me figure out what was going on and why typical chlorine levels weren't working.
I tried lowering CYA -- did some small partial drain and refills and also went through two separate does with 8oz packs of Bio-Active CYA reducer and then tried a 16oz pack of Bio-Active CYA reducer. I kept the FC level between 2 and 3 ppm for 10 days or more after each Bio-Active application. The water temps were between 72 and 78 while using the Bio-Active. From my measurements (4:1 dilution of pool water with RO water for the CYA test) the Bio-Active may have helped reduced the CYA level by 10ppm or so, but in general it has been ineffective. I plan on continuing with incremental drain/refills -- pumping the water onto the lawn and shrubs and disabling sprinkler system cycles appropriately to conserve water, to get the CYA down to less than 100, but was wondering what my target CYA level should be.
Separately, now and then I'd find a small bit of algae that I could easily brush off and decided maintaining low chlorine levels in the the hopes the the Bio-Active CYA reducer would actually work was a waste of time and was risky. I figured a shock/slam was in order.
Before Slamming numbers: FC 6, CC 0, TC 6, pH 7.5, TA 104, Calcium 630, CYA 130
Using what I think now was an outdated CYA/Chlorine shock table I read that 39ppm was a recommended shock level.
For all Chlorine tests I used the TF100 FAS-DPD chlorine drop test and the magnetic stirrer using 3 parts RO water and one part part pool water and multiplying result by 4 to speed up the test, conserve R-0870 reagent usage and avoid losing my mind by having to count out 80 drops of reagent. All measurements are FC, CC was always 0. If my reckoning on this testing method is incorrect, please let me know.
For all chlorine test results are FC, CC was always 0
The chronology of my slam follows:
9AM: - Pre slam FC = 6, TC=6. added approx 7 gallons of liquid chlorine and brushed pool
10AM: FAS-DPD test measured 40ppm (3parts RO water, 1 part pool water for FAS-DPD chlorine avoid having to speed up the test and conserve R-0870 usage), brushed again
12 noon: 26ppm chlorine - added another gallon of bleach after testing, brushed again
3 pm: 46 ppm chlorine (I must have screwed up the noon test), brushed again
5 pm: 44ppm chlorine, brushed again
8:45 pm: 34ppm chlorine, added another gallon of liquid chlorine after testing
10pm: 38ppm chlorine per test (last test of the day)
4:45 am (before sunrise) test measured 38ppm.
I see no evidence of algae in the pool, but this morning while perusing this site again and finding the pool calculator page, I noticed that for CYA at 130, it recommends
FC for shock: 51, FC for mustard algae: 69. Have I wasted a day and a lot of chlorine by slamming at too low a level of FC?
I'm now wondering if I should dump in another 6 gallons of chlorine and bump up the FC level to 70 for a day, or since there was no drop in FC overnight, conclude that I am done slamming?
If there were any algae, green or mustard (not sure how to identify the difference visually, but the bits I saw before the process seemed green) would the FC drop overnight even if I was only at an FC level of 38, or is algae so "tough" that no chlorine will be effective and consumed till I get the level to 70ppm at my CYA of 130.
I'd appreciate any suggestions as to whether I should continue with my current slamming cycle and escalate to 70ppm chlorine or, since there was no overnight drop in FC, I should consider the slam complete?
BTW, thanks for maintaining this most helpful and informative site and forums.