Mike,
You may have had less FC loss at the higher CYA. We're still sorting that out but it does seem to be the case. As for the algae you have, it sounds like yellow/mustard algae because at a CYA level of 40 it takes a minimum of 6 ppm FC to keep away and your FC sometimes dips below that. Yellow/mustard algae is heartier than green algae so takes more chlorine to keep away and more to shock. To shock it at 40 ppm CYA you need to first lower the pH to 7.2 (with acid) and then add chlorine to get to and maintain 24 ppm FC holding it even a couple of days with no loss overnight.
You are actually in better shape this year with your lower CYA because if you got this algae with your higher CYA last year it would take extraordinary amounts of chlorine to kill it (at 90 ppm you have to maintain 13.5 ppm FC to keep the algae away and 52 ppm FC to shock it!). You should wash your swimsuits in hot soapy water to prevent reintroduction of this algae though it may be getting blown in which obviously there's not much you can do about except keep a higher FC level. You can read other threads on this forum about yellow/mustard algae. I'm sorry you got it.
Richard
Bookmarks