My fish are always gasping for air no matter how hard I try or research to solve this problem. I heard it can be water parameters or not enough oxygen dissolving. I tried putting plants in the tank and they just turn black and die. People have told me it could be water conditions so I have started a RO system in the last 3 weeks doing a 25% water weekly change. The water change has put a little shock on my fish because of the pH drop I think. Before my pH was 8.6. My nitrates are at 30 most of the time. My temperature in my tank normally runs between 66 to 68. Feel free to ask me any questions. I can also send you a video of my tank. I would say I lose 1 to 2 fish a Month. The beginning stages of their death is when they start to lay on the bottom of the tank all day and out of nowhere they just die