I agree with what everyone stated above. I would never add untreated water to a tank. You can use spring water, but that can get pricey and add up quick. I reccomend picking up a bottle of Prime, it is highly concentrated stuff and can go along way. I beleve one cap full can great 55G of new water. Prime is a great product to help make your tap water safe for your fishes.
I also agree with the unreliability of strip testing. You can get the really nice liquid test kit made by API for around $25 at Walmart of my LFS. See if you can pick up one of these test kits and get a more accurate reading of your tanks water. There may be lying problems you can't see from a faulty test strip.
Also, what is the 55G stocked with and what kind of filtration do you have on it?