Hi, my name is Sean.
I have two firefish in a 20 gal
Marineland tank (I've had them for 4 1/2 months now) and one of them is breathing extremely fast/heavily and sitting at the bottom of the tank. The one that is sick has looked unhealthy since the day I got him but things have never been this bad. I noticed something was strange when he wouldn't come out for feeding time the past two days, so I started getting a little worried. Today he would barely move at all and was breathing how I described. I've suspected a worm for quite some time now because he never seems to get any bigger from eating and looks generally malnourished. I checked all water parameters I could test for (pH, ammonia, salinity, temperature) and they were all fine. I did a 30% water change anyway. More recently, I gave the sick fish a fresh water dip, hoping it would kill any parasite/worm that could be in him. I'm not sure how shortly afterwards symptoms are supposed to improve, but it's been 4 hours now and he's still breathing rapidly and sitting at the bottom of the tank. I'm not sure what else to do/what could be wrong with him? I don't think it has to do with water quality or something in the tank because the other firefish is perfectly fine... But they are a mated pair, it'd be so sad to see the one go :/