After the initial dose monitor the fish and if it shows no ill effects, dose this way (staying on the low side of the dosage) for two days rest for a day and see if the fish will eat a small amount of food. I adjusted the recomended dosage down as posted above because I don't want to risk kidney damage, which is the down side to using this. I'm trying to give you some chance of curing this guy. After everything you've tried this is really the last thing I can think of. I like trying the easiest and less risky treatments first before going to more diffacult or harsher treatments. I have also read about (never tried so can't vouch for it) treating the tank with Kanamycin wile administering the Neo orally, just an FYI. Prolonged use of antibiotics isn't good for fish or humans so I'm concerned about doing more harm than good but sometimes it is also the differance between curing the issue or watching a slow disintagrating death, which will surly happen if the fish doesn't start eating again. I'm having an issue right now with a wild angelfish that stopped eating and is wasting away. It hasn't eaten for weeks and is currently in a 10 gallon tank on Kanamycin. If that doesn't work I'm going to do exactly the same thing I suggested to you. Fingers crossed.