Possible black algae?


Bronze Supporter
Feb 27, 2018
Savannah, GA
I have read that it is not as likely on a vinyl surface but I think this is black algae. I brush it off and it reappears in the same spots a couple of days later. Water remains clear. Is any algaecide recommended or just more chlorine and brushing?
FC 7
CC 0
PH 7.6
CYA 60



Mod Squad
TFP Expert
Platinum Supporter
LifeTime Supporter
In The Industry
Apr 1, 2007
Sebring, Florida
Why does it reappear in the same spots?
Pretty much what tivo says. It slides along the pool floor until it settles in a low spot or a hump (like a liner seam) and that's where it gathers


Bronze Supporter
Feb 27, 2018
Savannah, GA
On further investigation it does appear to be dead algae. I went into the pool with a diving mask for a closer look. It brushed away easily by hand. The place where it settles is in the deep end near the corner. There is a return on the opposite wall pointed slightly down and towards the end wall so I guess it was creating a little vortex in the corner. I changed the direction of the return eyeball to see if it will have an effect.
If it is dead algae doesn't that mean that the chlorine level is effective? Do I still need to SLAM?


Well-known member
May 27, 2016
Berkeley Heights, NJ
So those spots were "easily" removed with hand / handbrush? I may have a same issue and my son continuously brushed those spots (e.g., 2 mins each) but nothing.....just opened the pool and can't get in yet but "scary" as we installed a new liner 2 season ago. We actually had mustard / brown algae around same areas with the old liner.