Sand Rubbing

[rfdoc]

I've had two false percs for a couple weeks now along with a clean up crew. The fish look fine to me but every once in a while I see them both rubbing their sides along the sand at the bottom. Is this normal activity or an indication of disease? I do not see any spots on them and they both eat well.

 

[ahoyhoy239]

my percs do it too especially at night. for some reson my clowns wont host anything in my tank, they just sleep in the sand in the corner and have been like that for about a year now so im pretty sure its normal