They're cute to watch, but don't help that much...
I have shrimp in my tank (lil hitchikers!) and had mollies in there, and it was a 10 gallon. Even with regular weekly water changes/vacuuming, OH MY GOD every time I do it all this poop, debris, dead plant matter, etc comes flying up like I left them for a month.
Mollies are very messy, and someone needs to start vacuuming that gravel out before it builds up and becomes toxic!
Kaida- CT Female 2.5 Gal.
Julep- HMPK Male 2.5 Gal.
Fandango-HM Male 10 Gal.