I got a 38 gallon tank to put my rainbow shark in...he was in a 10 gallon with other fish originally and someone told me that is a big no-no. So he is the only fish in my 38 gallon tank. I have had him for a few days and he likes sitting behind my quietflow filter for pretty much all hours of the day (until I cut the lights off, at which point he swims around quite a lot). I made an overhang out of shale and have 5 medium sized live plants in the aquarium, but he chooses the filter.... He liked the filter in the 10 gallon too. This tank was very recently set up and before putting him in, I made sure the temperature was around 75-78, the PH was about neutral, and I put in live bacteria to aid in the cycling process. I also put in stress coat, though he doesn't seem to be stressed with all the swimming he does with the lights off. I also never see him eat. I use fish flakes, and I have yet to see him try it. I have not seen him nibbling on anything....nothing. I am going to buy some algae pellots today to see if he tries those. So is it okay that my rainbow shark chose the filter as his hiding spot? And is my shark eating at night when I am asleep? He seems pretty healthy. He never looks encouraged, but his stomach is never concave either... My original thought about the filter was maybe a lavk of oxygen, but I have several live plants that should be doing their job, as they are alive and well.