Algae growth with high FC?


Mar 11, 2017
Round Rock, Texas
Hi all,

I have what appears to be an algae problem in my SWG pool with a high FC. Each week when I brush the pool I have a little greenish tinge on the walls and when I brush tiers and the bottom I can clearly see a cloud following the brush. The problem is that I keep my FC values high enough that this should not be possible I thought. This week it was even worse so I decided to SLAM the pool which I just started. Here are the current water parameters: Free Chlorine: 7.8, Combined Chlorine: 0.0, pH: 7.8, Total Alkalinity: 70, Calcium Hardness: 280, CYA: between 40 and 50, closer to 40, Salinity: 3600. SWG is running at 50% and pump is running 12 hours a day. We have had a little more debris than usual in the pool recently, but I would have have thought that the
chlorine this high would still prevent the algae growth. Can someone comment on what could be going on? Could it be something other than algae? If it was just the bottom surfaces, I might blame something like pollen or something like that from the trees, but it's on the sidewalls too so I would think that's unlikely. If it's truly algae, how can I be having this problem with these water parameters? They seem reasonable to me. Thanks.

Rancho Cost-a-Lotta

Silver Supporter
Apr 10, 2018
Rancho Cucamonga, CA
I went through the same thing a few weeks ago. I had my pool covered for a few days and found algae growing on the walls when I removed the cover. It seemed to grow in areas having the least amount of circulation. Water chemistry didn't indicate any problems and FC levels were higher than needed for my CYA. After my SLAM, I followed the mustard algae recommendations and have been keeping FC elevated. So far, no issues, but I'm too paranoid to cover the pool for now.