I have a 35 gallon tank with 2 jack dempseys and 2 tinfoil barbs. They are around 3 years old and have grown up together. Recently one of my jack dempseys (the bigger one) has been hanging at the corner of the tank. He does that all day. It's not his usual behavior. He's a very active fish. Any suggestions? I live in an area that doesn't have chlorine in the water. I still use Ph tablets just to keep my tank balanced. The temperature has been 70 degrees. Jack dempsey doesn't look different in terms of its scales or looks unhealthy. What is wrong?