I have kept discus on and off for about a year now. I started doing water changes once a day until I learned that it can be a waste.
I now have 4 discus in a 72g. I feed three times a day(feed four when they were younger) and I water change every two or three days. They follow me around and seem to be doing great. And they do much better with 3 or 4 or more. A 55g is big enough easily for five or six. Although they need open swimming space, tank size recommendations are sometimes more aimed at keeping more stable water parameters. In a 55g, I would do more water changes because their is less volume and it will possibly be less stable than a 75g or larger.
Good Luck
*edit* remember the more other fish you keep, the less discus you can probably keep. So with corys and tetras, you may want to keep the number around 4 like mentioned earlier.
I'm a little surprised to hear 20-25% daily... mostly because the websites I've read (NEVER trust everything on the net...) suggest 25-30% 3 times a week, but I have no intention to skimp out on maintenance. I want this fish to be healthy and happy. :grinyes: Oh, and thanks for not jumping on me for only having one atm. 
