Been fighting black algae for a while. Started letting our FC levels drop after we had several nights with no FC loss at FC shock levels.
Finally was able to afford the test kit with CYA test and discovered our CYA level was 100, not 50 like the pool store said. Today I did another partial drain and refill to try to get our CYA level down but it only brought the CYA down to 70. I'll do another partial drain this weekend to get it down to 50 but for now I am working with a CYA of 70.
I've been doing morning and evening FC tests and I'm not sure if I should be bringing the FC back up to shock levels instead of continuing to let it drop. We have started losing FC overnight but in fairly small amounts. But since I'm losing less during the day than I am at night I am very unsure what to make of this.
9/30 - 10/1 overnight lost 1 ppm (19.5 to 18.5): overnight low temp 57
10/1 - daytime loss 0.5 ppm: daytime high temp 93, pool partly shaded most of day
10/1 - 10/2 overnight lost 2.5 ppm (18 to 15.5): overnight low temp 56
10/2 - daytime loss 0.5 ppm: daytime high temp 78
Thanks for any guidance.
15,000 IG White Plaster Cart Filter Jet Vac sweep, new pumps and filter system this year