My betta will swim once he sees us but when I glance at him he usually is laying at the bottom of his tank lately. I have a thee gallon tank with two nirite snails and a moss ball. I use a baister to take the water from the bottom and usually only do a 25% water change one every two weeks. He doesn't have any signs of illness on him other than he is staying on the bottom more than usual. He is eating normal. I usually only give him the most of three pellets a day. What do you think is going on?