I have 2 of them that get suction cupped to the glass. For starters I always place incoming fish into the box after acclimating them so that I can see that they are swimming well and usually only hold them there until they eat. I will release them after the lights are out. I recently had an online retailer tell me that it was too stressful on the fish and was the cause of death of the fish I bought from him. Don't buy that story but figured I would present it.