due to chlorine consumption I assumed I had algae (hard to tell as I have a black-bottomed spa).
it's an 1100 gallon spa with vanishing edge and overflow basin (300 gallon).
current measurements are
shock FC 16
All other levels are balanced
I'm losing 9 FC overnight even though the water is sparkling clear. I've been slamming since last sunday (5 days) Any thoughts on what's going on?