So I have a 29 gallon tank and a few of my fish, my gouramis, platies, and mollies, always charge the glass when I turn my lights off. They are the only fish in my tank that do that so I'm just wondering if that's normal behavior for them. They've been doing that since I got the tank about 2 months ago. Sometimes they hit the glass and sometimes they stop just short. Could this be an issue or is this fairly normal?