Black coraline or something else?

gobirds4290 · 2026-10-02T12:31:11-0400

My tank is a year and a half old and I’ve got zero pink/purple coraline growth. What I do have tons of though, is this black growth that covers nearly all of my rocks. Is this coraline that’s just black or is it something else? I tried scraping it with a tooth brush and blasting it with a turkey baster but it won’t come off.

Randy Holmes-Farley · 2026-10-02T12:38:32-0400

Might be a sponge. Doesn't seem likely to be coralline.

keagan · 2026-10-02T12:45:21-0400

+1 encrusting sponge

gobirds4290 · 2026-10-02T12:54:20-0400

Randy Holmes-Farley said:
Might be a sponge. Doesn't seem likely to be coralline.

keagan said:
+1 encrusting sponge

Anything to be concerned with or try to remove? Knock on wood I haven’t noticed any negative effects with it so far

keagan · 2026-10-02T13:00:03-0400

gobirds4290 said:
Anything to be concerned with or try to remove? Knock on wood I haven’t noticed any negative effects with it so far

If it gets stressed or starts dying off theres a chance of toxin release so run carbon if it starts declining. It looks like a cryptic sponge it's growing very low on the rocks so I doubt it'll cause any issues. It looks nice enough personally I'd keep it and monitor it.