BParker

since i bought these 3 guppies all my fish swim really fast up and down this one side for the tank when i turn my light off, is thi normal?

agabr123

it sounds fairly normal to me. i'd test your water just in case. what fish are swimming rapidly? the guppies? or the other fish since you introduced the guppies?

Llama

Mine used to do that too for some reason. Probably looking for algae or seeing their reflection and tryign to work out what's happening.

BParker

its just guppies and the odd white cloud minnow

COBettaCouple

It can be a variety of things, but it's not uncommon for livebearers to do that. Testing the water to be sure is a good thing and I think aeration never hurts.