Black Algae


New member
Sep 21, 2018
Miami, FL
We completed construction of our in-ground pool in May 2019. We started out with liquid chlorine and switched to the SWG this past April. I have been struggling to raise the CYA. It had been at 30 up until 2 weeks ago when I noticed a spread of black algae in my pool. We have been brushing 2-3 time a day and kept the pump and SWG running 24 hours. We tried adding Algaecide 3 days ago for black algae but all it did was make the water cloudy. I was recommended to add Chlor 90 or scrub with the chlorine tablet. Any suggestions?

FC 3.5
PH 7.6
TA 80
CH 300
CYA 60

Texas Splash

Mod Squad
TFP Expert
LifeTime Supporter
Hello and welcome to TFP! :wave: If what you see is actually Black Algae, it can very tough to remove. But regardless of which type of algae it is, the first action required is a SLAM Process. That's #1 by using a proper test kit - either a TF-100 (link below) or Taylor K-2006C. SWGs are not designed to maintain the elevated FC (SLAM) level as noted on the FC/CYA Chart, so give the SWG a break and maintain the required FC level with liquid chlorine or regular bleach until you pass all 3 SLAM criteria. Do not add any algaecides either. If it's copper-based, it will not come out unless you change the water. Alagecides don't kill algae anyways, for that you need chlorine using the links noted above. If you already have a TF-100 or Taylor K-2006 tets kit, please list it in your signature as well. Good luck!



Gold Supporter
Bronze Supporter
Jun 11, 2018
Verona, MO
Sounds like your swg too small, like mine. You need to supplement liquid chlorine to maintain safe levels.
FC 3.5 and CYA 60 is not a good combination.
Review the chlorine/cya chart in pool school.