Can anyone who has had experience with Gymnothorax tile give me some pointers?

I bought a Gymnothorax tile a little over a month ago and for the most part he stayed hidden and only out when the lights were out he would flee back to hiding when the lights came on. I have had others that acted a certain way before passing on. This one is exhibiting similar behavior but the red scat does not bother him like it did with the others that passed soon after acting this way (the way fish attack other fish when sick) which seems to indicate he is not in immediate poor health. I hope I am over reacting to what maybe normal but seemingly long acclimating period. He also does not swim to the top to poke his head out of the water which is probably another good sign.

Can you tell from normal breathing from heavy breathing that should raise concern? The main concern is his lack of trying to hide like he does not care anymore. I have not actually seen him eat but do not know how long they can survive with out eating. He maybe just out looking for food but has paid no attention to the guppies swimming near him or just decided to make his somewhat new home finally home and swimming out after accepting the change from one location to another.

I was considering trying to get some bull minnows from a bait shop to see if he would eat them. I also have a toad fish that bull minnows would probably be better and more substantial than guppies and ghost shrimp. Can anyone suggest some other types of live food I may try for the G tile?

I took my water sample to have it checked and all that showed up was that something was high but not considered toxic unless exposed for long periods of time. I had t put on a new filter so this could have caused this to happen but it would not account for the behavior. Most likely the big guy was just hungry. I put some ghost shrimp in so now he is breathing fine but still staying out a lot but now he will try and hide if lights are turned on. I am using 3tbl spoons of salt p/gal. I forget what they said of my salinity but it was fine for brackish.

He seems to be doing very well now. I think the combination of having to replace the filter as it cracked on me changed the water conditions. I am using an aqua clear with the ammonia remover and with everything being new and him being hungry at the same time. It appears he is eating something even though I have never seen him actually eat.