My never-ending SLAM finally ended after several weeks for the 2nd year in a row - or so I thought...
It started back in mid-March, with the yellow/green algae. Testing showed low CYA and of course low FC, so I got the CYA up into the low 30's over a coupe few weeks while keeping FC in the mid-high teens which I thought was appropriate SLAM level and was getting nowhere fast.
TA and CH have been steady around 120 and 300, no CC's then or now, and pH was 7.8 before SLAM, 7.2 after, and now is 7.4 after some borax last week.
After about 3 weeks of this I got sick of screwing around and dumped a bunch of LC in, up to 22 or higher.
Not quite 2 weeks ago it crystal-cleared up and passed the FC drop test 2 nights in a row so I let the FC drift down. With daily drop testing it got as low as 4 before I added LQ to keep it around 5, knowing the FC/CYA chart is a guide and pools will vary - this is when I added the borax. I noticed a yellow tinge 3 days later and ran FC up to about 8 and have kept it above 6 for the past week.
I installed 320sqft of solar pool heating panels 3 days ago and have put 8* in the pool since then (not bad with the array in full shade by 4pm!), today I see yellow "dust" and have run the FC back up to over 20 to knock this out.
My question, finally, is how far off can my pool be from the recommendation of the FC/CYA chart? With CYA of 30-35 is it reasonable to have a min FC as high as 6 to keep the algae from getting started? Is there some other chemistry in play here? It's been at least 20 years since the pool was built and never resurfaced.
CC=0, pH=7.4 (tested before FC run-up over 10), TA=120, CH=300, Temp=86*.
I have the pool stores check my water just for poops and grins whenever I buy LC, supposedly my phosphates were 1900 6 weeks ago, then 1000 a couple weeks ago, and now they're down to 300 - now I'm certainly not running out to buy phosfree, but I know it becomes available to algae as food at some point.