Hi - was starting to get some algae building up on the grout on my waterline tiles, so decided to go ahead and SLAM the pool. I'm using the TF-100 kit.
Numbers before the SLAM:
I added 1 qt of MA to lower my pH, set my target FC to 24 and added the expected amount of 10% chlorine around 7:30pm. Brushed the pool and tested at 9pm last night after sundown, FC was 26, CC <0.5. Retested again at 5am this morning before sunup, FC was 24.5, CC <0.5. As I was at work all day and not able to monitor/add chlorine, I added 1/2 gal 10% at 5am aiming to bring the FC up to 28 to allow for FC loss during the day and still be above the 24 level. Just retested at 4:30pm and my FC is down to 17.5! So I've lost ~11.5 ppm in <12 hrs.
Trying to reconcile the results from my OCLT which indicated only 1.5 ppm lost over about 8 hrs. If I scale up the OCLT test it means the chlorine load from breaking down algae/whatever is about 2.5ppm in 12 hours, and puts my sun loading at 9ppm in the same period....it's been hot and sunny all day and the pool gets full sun from about 10am, but that seems like a really high FC loss. Is it to be expected that you simply get more FC loss when the levels are high during a SLAM? I'm reasonably confident in my CYA numbers, they have typically been in the 50-60 range. I'm reasonably confident in my CYA testing, and the pool store gets similar numbers. Certainly my CYA is no lower than 50.
I didn't have a lot of visible algae buildup just small amounts on the grout in some places, I'm not dealing with a swamp. Water is clear.
Any suggestions / advice? If I don't pass the OCLT tonight, I'll have to add much more 10% tomorrow before I leave for work, to make sure I stay above shock level all day. Based on today I'll need to aim for a FC level of 36....!