Water parameters are the measurements of Ammonia, Nitrite, and Nitrate as determined by your water test kit. If you don't have a test kit, take a sample of your water into the fish store, they will check it for you for free. Write down the numbers they give you, don't just let them tell you it's "fine." No, fish won't build up an immunity to fin rot. As I said, this is a water quality issue. You need to be doing regular water changes. Read my website for tank cycling information so you can get a grasp of what we're talking about here.