I've had this little guy for about 3.5 years and lately noticed that he spends hours at a time, gasping at the surface. He began doing this in spurts several months ago but for the last several days, he's kept himself wedged up against the filter intake. I've found other forum posts where people mention noticing similar problems but many of these were attributed to having aquarium salt in the water (I don't use it) or poor water quality (ammonia & nitrite = 0, nitrate = 15ppm). Tonight he's barely moved and this was the first time he's shown no interest in eating. Can anyone recommend something I can do which might help him?