Am back, all stuff previously discussed underway. FC now 8 and will gradually exchange water to lower CY from 80. Rainbow set to zero. Cheap generic bleach did raise the pH now fixed with acid.
New question about algae.
Brushed today. On the sunless walls found a few small areas (few inches in diameter) of yellow brown color that brushed off easily and made a vague cloud and was then gone. Water is very clear, can see all the plaster defects. Is this algae? Yes No.
If yes, should this never happen? Or is this how it is from time to time and you just brush off (so to speak) and move on?