It would be nice to know how big this piece is. I get the impression its extremely small - and there are numerous things going on. It looks like there is hair algae, a macroalgae of some type. etc/. I would suggest you take the rock out - after shaking it a bit - to get the polyps of the GSP to retract - then get rid of the rest with a soft (key word - soft) toothbrush. Rinse with tank water (into a sink) and replaceI think these are hydroids but idk, they are kinda cool but I think they are affecting my gsp, any help
