No offense but your water change is really not suitable for discus. Biological filters do not remove nitrates, they create them. Discus don’t like nitrates persistently >10. A 20% weekly water change will have your nitrates constantly climbing and your discus will suffer. Your water change schedule needs to mitigate the nitrate production in your tank for the discus to be healthy. If you started w adult discus and every other week could do a large 90% water change to bring your nitrates right back to near zero it may work. Unless your source water is poor quality you actually don’t need RO, even for wild fish, but especially domestics and they are very tolerant of even high pH & high TDS water. The big things that harm discus is ammonia & nitrite which the biofilter deal with, but also nitrate which can only be removed effectively by water changes, not the filtration.
Your cleaning lady might wait if she’s paid by the hour
Hope this helps!