Is this normal ??

[lee&carter96]

Hi everyone I hope you are all well. Yesterday I finally added a cleanup crew to my fluval evo 13.5 to deal with my diatom issue. I got 4 hermit crabs and 4 snails. Since then I have noticed lots of dark looking dots/degree across the sandbed. Is this normal? Or something to worry about? I will post a video of it, appreciate anyone's opinion thanks in advance.

 

[lee&carter96]

 

[dedragon]

probably snail and hermit crab poop. Try increasing flow so more of it gets blown into the filters