Organism ID

[BubblesUp]

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?

[hillegom]

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?

[BubblesUp]

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!