I got this puffer a few weeks ago and he is in a temporary 10 gallon tank and is about to go into a 30 gallon. Ever since I got him, his belly is dark all day. When i first turn on the light in the morning, it is all white. After a few minutes, it goes dark again. The salinity is 1.004 and the temp is between 77 and 81 degrees. I have been feeding him mealworms, shrimp pellets, and feeder shrimp. Im about to get snails for his beak though. So what would make him be stressed?