Does anyone know what this is?

[lbass]

I've seen this in my tank lately, and I have removed it once but it is back again and wondering what it is!

[StudentoReptile]

All I see is rocks in a tank.

[Starbuck]

is it an aquatic tank? what kind of animal?

[poison123]

Talking about the little crumbles on the floor?

[Amadeus]

Assuming it's a turtle it's probably little pieces of shell and crumbled food.