LittleBlueFishleat who helps on your thread is very knowledgeable and i value her opinion a lot. So if you want give us update in your thread. My personal advice is take the filter out and do daily water changes if you can. I know your tank is big though. You can lower the water so it will be easier for you. I would do 50% water changes for a few day follow but full water change.
If he got worse or more symptoms i would try to treat him with aquarium salt unless he is bloated or constipated then Epsom salt is helpful.
Also did you check if his scales raised. If you look for the top down see if he is pineconning .