SantaMonica;2465372; said:That's the problem right there. It's been way way way too long... I thought you'd been cleaning weekly. The underlying layers are dying from being shaded by the new growth. I've seen it now several times on several screens from different people. It's surely adding ammonia to the water. I'd clean the whole thing, then clean alternate halves each week.
There are no "layers" the algae is about 1/16" thick. I could wipe it, but I doubt this is the issue after looking at some of the harvests you guys have done.