I was maintaining the pool at FC 6 (PC says FC 4-9) and started getting spotty algae breakouts. Shocked and raised the FC to 8 and the algae dissapeared for a while. The it appeared again in the the same spot and its vicinity which is near the spa spillway next to the steps of the pool (shallowest part of the pool). Shocked, and raised the FC to 10 and algae dissapeared again only to reappear as soon as i brought down the FC to 8. This time it appeared in other parts of the pool also.
Here are the parameters of the pool when i got the last algae:
CC 0.25 (barely pink solution)
Last night I raised the TA a bit and have started shocking the pool again. the temperatures in this whole scenario has been rising and the last outbreak of algae was a few days into the heat wave with pool temp 87 F.
Also the CH has risen from 290 in June to 390 yesterday. Pool has been needing water but just like last year though.
Above all, this season we have used the pool only once! So there has been no bather load around the times of these algae outbreaks. There has been no change in circulation rate or pattern.
I must admit that I had been letting FC drop to 4-5 before these outbreaks but that is still within range according to the pool calculator.