Black splotches in their sand

[Gorillaz6276]

What is the black splotches in my sand? Is it their poop? I have A LOT of isopods in my tank, does it have to do with them? I took out a fake plant and this is what was under it.

[Gorillaz6276]

This is what it looks like

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[hermitcrablover2]

Do you use a mix of coco fiber and sand? If you do, maybe the sand was moist and bits of the coco fiber got clumped together???

[Gorillaz6276]

I just use sand

[wodesorel]

Unfortunately the photo isn't super clear, but what you're describing sounds like poop. Mine always leave it in and under the decorations, including plants. Fresh stuff will look like chocolate sprinkles, but it breaks down and will eventually just become darker patches of sand.