Organism ID
 

Old 50 gallon tank. Growing on one of those old-style thermometers that bobs in the tank. I have not noticed tentacles or anything like that. Colour is cream. Anyone have an idea what these are? :wink:

It is really hard to tell as its kind of blurry and too blue.
So I am guessing on pinapple sponge, though they like dark corners better.
Harmless filter feeders. How long ago did you start this tank?

Thanks for your reply. You are the second person to ID it as Pineapple Songe. From the pics online it looks like you are right. I just took a look and they all have seemed to vanish. I recently installed a new light and strong canister filter. The aquarium has been running for about 7 years. It had a hard crash from a power outage about 5 years ago and my Fluval canister died about 3 years ago. Things are turning out for the better!