08/04/2026
Would you know how to spot Black Algae in your pool? Our tech found this on a client’s pool last week. Most people would’ve walked right past it.
Those little dark spots in the plaster are black algae — and it isn’t actually algae. It’s cyanobacteria, which is why it doesn’t behave like the green stuff.
Green algae clouds your whole pool and shocks out over a weekend. Black algae does the opposite. It stays small. It stays put. It looks like nothing.
Meanwhile it’s rooting down into your plaster and building a protective outer layer that normal chlorine levels can’t get through.
That’s why scrubbing it off doesn’t work. It looks gone. Two weeks later it’s back in the exact same spot, because you took the top off and left the roots.
It hides where nobody’s looking — shaded corners, steps, grout lines, behind the ladder, around the light niche. Low circulation, out of sight.
Caught at this size: a stainless brush, targeted treatment, a few follow-up visits.
Left alone for a season: draining, acid washing, sometimes replastering.
That’s the difference a trained professional makes when caring for your pool. It’s easy to spot a green pool, but often times the biggest problems can be the hardest to see.
If your pool has dark spots that won’t brush away, send us a photo and we’ll tell you what you’re dealing with.
📍 Serving Wake County
