yeah, I hate to be the bearer of bad news, but Idols are very touchy to fluctuations in water quality. Temp, pH, salinity are all factors that really affect them. In keeping an Idol, I would definitely make sure you have a refractometer and good test kits to know what your water parameters are. I would pick up Salifert kits so that you know your water is good. You want to make sure you have a pH, kH, and nitrates test kit so that your levels stay in tact. Many people do not know to test kH, but with an Idol, I definitely would make sure you are on top of everything. This is especially important when you are doing a water change. When you do a water change, make sure the water temp. is exact, as well as the specific gravity. Give your new saltwater at least 24, but preferably 48 hours to sit and dissolve before you do all of your water changes. Like I said, any fluctuations in the water quality could cause your Idol to stop eating, and then that might be the end of it.
Also, is your only form of water movement your main return? If so, I would probably look into getting a powerhead to put a little bit more circulation into the water. That way, your nitrates have less of a chance of building up.
Good luck with him though. The fact that he is eating is definitely a step in the right direction. Just keep your levels stable and hopefully it should stay that way.
