Hey! There’s !aquariums, !aquariums, and !aquariums. The lemmy world one’s a bit more active, but I don’t care, I just subscribe to them all lol. I haven’t found a substitute for r/PlantedTank or r/Aquascape yet though. Someone’s created !plantedtank, but it’s dead.
Edit: I just realized there’s !reeftank and !ReefTank if you like saltwater!