So I recently took a 5 day vacation and returned home to an algae bloom. I don't have the exact numbers in front of me, but I do at home. CYA was around 25 so I boosted the FC to shock levels (10-12 ppm) with liquid chlorine, filled the chlorinator with Trichlor and set pump run time from 10 am to 8 pm before leaving Monday evening. Wednesday afternoon, my BIL checked pool (10 ppm FC) and attempted to vacuum. Unfortunately a skimmer line leak complicated that but that is a different story. Since the FC was fine he left it as is. Fast forward to Saturday morning we arrived home to a green monster but measured FC still at 6.5 ppm ~ 12 noon.
The pool was covered with blue solar cover the entire duration short of the vacuum attempt. Skimmer line was off and plugged so main drain was the only pump inlet open. I have no data to certify that I didn't drop below the minimum FC during my time away, but assuming I generally only lose 2-4 ppm of FC on a normal day with the cover off and without pucks in the chlorinator, I have a hard time believing that I fell below the minimum.
I know no way to quantify, short of experimentation, just how much and how fast FC is added via my chlorinator. Additionally I cannot estimate normal FC usage during the day with the cover on blocking UV rays. But assuming that I was in a downward slide with FC from Day 1 foward (debatable), I know the chlorinator would not have added 4.5 ppm of FC from Sat. at 10 am until Sat. at noon when I tested it at 6.5 implying that I was not below the minimum.
While reading the "Determining Pump Run Time" article, the sentence "One thing to keep in mind is that pump run time does not prevent algae, only maintaining a proper chlorine level can do that." stuck out. Yes only free chlorine can prevent algae, but what part does circulation play? Assuming that the chlorine finds a happy medium and is evenly diffused throughout the pool, how oh how was there an algae bloom??
I have had several bouts with algae this year and being a first time pool owner I have learned many lessons along the way. I have read several articles on covers maybe or maybe not contributing to algae growth and that covers prohibit gases from venting, but I wanted to start a new thread for help.
Any ideas or comments would be welcome. Oh, since that time I have completed SLAM and levels are leveling out. All readings are with the trusty TF-100. I will post numbers in a few hours. Thanks.