You have to do it exactly as it is said. At the end of the thread I quoted, there is a correction in the dose to 2 tbsp to each 10 gallons. I add 6 tbsp to my 30 gallon tank, so it is around 3 ml to each gallon approx. Maximum would be 1044 ml (4 tbsp per 10 gal) but in your case would be 522 ml. That is for H2O2. Plenty, plenty, plenty of flow. Remove the filter media from your filter and run it on water change day. If you have any other powerhead, put it in and run it also. Add H2O2 and keep it running for 15 min. Then do a 50 % water change (with all filters and powerheads running) or more and when tank is filled again add excel at 5 ml to 10 gal, so around 90 ml in your case. Now you can stop all the powerheads and filters. Put the filter media back in and run it as you would do normally.
I do it with fish inside. None has died that I can undoubtedly associate to this treatment. Actually I have 2 ramirezi and I have done this treatment for, at least 3 times, and they are fine. If you want to remove your discus, that is OK. But you can do the treatment with them inside or add them next day if you want to allow for the excel to be inactivated.
Only thing is that you need to be careful with shrimp if you have them (discus and shrimp... I guess you do not have that problem 😉😉😉).
