fish tank looks rusty

Question
i have been having some trouble with my 30 gallon freshwater fish tank. its a community tank with 1 male betta, 1 spotted garami, and 1 jelly-bean parrot fish. the parrot fish is separated due to it attacking my other fish in the past. my betta fish has been getting fin rot often, it starts to get better-fins start healing and growing back- then within a day hes back to looking sick. i have tried using a fungus eliminator which seems to work for awhile. he just seems to not fully heal-this would be 5 times he has looked this bad. not only this but after my last water change-only did a 50% change- the side with the betta has a rusty look to it. the sides the bottom everything and it has grown at a pretty fast rate. i use a water conditioner and have tested my water a number of times and it comes back perfect. i just dont understand.

Answer
well it sounds to me your fish gets stressed out in the middle of healing. is your beta separated? if not try separating him and continue treatment. make sure his new tank has good water quality. Let him stay in this tank till his fins look like they have grown completely. after you think they have grown to their regular size keep him in the separate tank and monitor his behavior. does your beta have clamped fins? stay at the bottom of the tank? how often do you change their water? rusty? does it come off easily?
corinna