there are people on this forum far better qualified than me to answer
however some simple advice jumps out at me
- stop adding all the crap
- switch to RO with a re-mineraliser
- switch to daily water changes...with problems i'd be looking at 50% daily
- tell us more about the setup - what else is in the discus tank(sorry i got confused half way through reading your thread) and how is it setup (subtrate etc)
- start courses of meds recommended here, i'm not familiar with the ones you stated