Actually water changes aren't stressful to fish but benificial... I Do 30-50 % in all my tanks about every 5 days. When I Do big cleans can be up to 75%( everything out of tank but fish). Your benificial bacteria is in your filter media mainly and your substrate, NOT the water. Try feeding some blanched deskinned peas. ( or green beans) either one can be soaked in some garlic with helps with many ailments.
"Why does Sea World have a sea food restaurant?? I am half way thru my fish burger when I realize, OMG I could be eating a SLOW LEARNER!!" ~Lynda Montgomery