Sandy Bettas?

[LyraGuppi]

Sometimes I turn on my fish light for a few minutes in the middle of the night to check on my fish. I currently have 5 bettas in my 20 gallon (along with cories) and most of the time, they sleep on the bottom of the tank. A few nights ago I saw sand, yes, sand, on my bettas. In the morning the sand is all gone. Is it just from the cories stirring up sand onto my bettas?
 
Note: It isn't a pile of sand, just a few grains.

 

[PrairieSunflower]

That sounds like the most likely scenario.  If it looked like grains of salt and didn't disappear I'd worry it was ich.

 

[betta fish]

I wouldn't worry about checking them in the night, because fish don't have eyelids sudden light will startle them, but yes I'd imagine the cories are more active in the dark and they are stirring the sand bed up onto the bettas 

 

[LyraGuppi]

Oh, okay, just wondering,