Looking for clarification. Shocking pool for 3 rd time now due to small yellowish green algae spots That disappear initially with regular shock, easily brush away only to reappear a few days later on all but south facing pool walls in pool despite chlorine levels have never lowered below 11 ppm since last shock and no free chlorine loss overnight , 0-<.5 cc and clear water. Filter backwashed regularly. Current levels are:
Cya 80 ( lowered from 109 by drain and partial refill )
Cl 14.5 but bringing it up to 22 tonight
Salt 2900 (need to add more I know)
Yesterday Pulled out pool light and scrubbed hidden algae there and will get ladder/ floaties treated as well. Pool was green swamp when we opened 2 months ago butwe thought we got it all but apparently resistant algae is in there still.
Question is if algae doesn't show up for several days after I brush and there is no fc loss how do I know when to increase chlorine to mustard algae level (44 based on my cya)?
Pool store tried to get me to use "no staining" copper algaecide but I'm not going down that road!
Any help appreciated!