the blob

This blob of gray stuff has suddenly appeared in my 10 gallon aquarium where my kids' comet goldfish has been happily living for 6 months. I've also started to see some green algae form along the glass and filter intake. I'm considering adding a few snails to eat the green stuff, but this gray blob has me spooked!

2 Answers 2


I am going to take another guess and tell you it looks somewhat like a decomposing residue of the inert material that is sometimes used to attach potted aquatic plants to their pots. It could be the case if you've recently bought any of these.


I will only have to guess, but I think it is a biofilm; most of the surfaces in a tank are covered by a thin layer of bacteria.

When the bacteria layer comes loose it looks like the stuff you have in your tank. I do not think it does any harm in your tank.

If this is in a place with a lot of dust, it might be from the surface of the water too; no matter what it is, you might want to remove it from the tank.

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