Hello trailshredder and welcome to FTF. I do not add anything to my Discus tank. I have well water just for them that is very soft and it suits them perfectly. I have never had any issues with water and am a firm believer that the less chemicals you can add, the better. IMO I would add whatever I was going to add to the water prior to adding to the tank just to ensure that it is thoroughly mixed. Could be my saltwater training, who knows! What is your water source/water readings? How many are you planning to have in a 55 gallon, and will it be a species tank with no other fish? Please tell me you are planning to complete a fishless cycle? Are you going to have live plants? Discus like it quiet and to have places they can hide out. I have some photos of my 75 Discus set up on my user page. Good luck and keep us posted. We're here to help however we might.
__________________

200 Amazon
Discus, Angel, Rummy Nose
Nano
2 Percula Clowns, 1 Chromis