Hi, been following for a long time and been able to take good care of the pool for around 10 years. This year for the first time I am having a disaster opening the pool because I don't know what the issue is. I have a very tough (almost impossible) to remove algae, there are green sections, white? sections and even darker blackish dots. I thought for a bit it was black algae, but I can not scrape anything off with a finger nail to see if it smudges green. What is there almost seems more like a spilled old paint or something which has me concerned it could be scale. Never seen it before. I've been scrubbing with a stainless steel brush and that doesn't appear to make measurable progress. I suppose there _has_ been very slow progress, there are patches showing through the mess that is clearly the actual pebble finish color I'm used to. When I scrub I do see clouds of grey/white/green come up so it does seem like an algae, but not much so maybe a combination of problems.
FC: ~15
pH: 7.5
TA: 50
CH: 280
CYA: 40
FC: ~15
pH: 7.5
TA: 50
CH: 280
CYA: 40