Treating Black Algea spots with Bleach Gel?


New member
Sep 26, 2017
Issue: I am getting a crop of of the black algae dots in the plaster in random places around the pool. Typically no bigger than a 1/4" in diameter.
Background: The pool cover is new this season. The cover really keeps heat in it in (an aside: If you don't have a cover, it is really no trouble to use if you get a cover reel, and really make the pool temp comfortable. )

Results: As a result of minimal Chlorine dosing + warmer water than last summer after adding a pool cover, the algea spots show up.
I want to try to use a Bleach Gel product used in bathrooms to see if I can pinpoint deliver chlorine to the spots of black algae.

Question/ Solution:
Does anyone recommend or not recommend using a product like Clorox Bleach Gel to spot treat black algae?
The product I saw contains the following chemicals:
1) Sodium Hypoclorate (bleach)
2) Sodium Silicate (???? not sure what this does )
3) Surfactants (not excited about making bubbly water)
4) Sodium Hydroxide (coincidentally used to increase PH. Although my water chemistry doesn't need it.) :
The slime coating of the black algae would be constantly attacked by the gel placed on the algea. It will deliver a concentrated dose of chlorine & sodium hydroxide to the algea. At least that is my hope or hopeful logic.

I"m open to advice...


Silver Supporter
Aug 22, 2017
West Palm Beach/Florida
Pool Size
Salt Water Generator
SWG Type
Hayward Aqua Rite (T-15)
Your first and best bet is to follow the advice listed by Marty.

The key is to scrub the black algae often. A stainless steel brush is best. I use a mask and snorkel and get down there to make sure I got it. I even use a small bamboo bbq skewer to pick at the spots. If you want to go even further, after the scrape a turkey baster will some 10% squirted right over the spot will help direct some high dose there for a short time.

Then again follow Marty's advice.
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