From what I understand, the chlorine, which is what you are removing mostly from the tap water, will not instantly kill the fish. So, treating the water after it is added or during (as in with the python) would be ok. I've been looking into buying python because I just got a 36 gallon. (doing water changes with a 10 gallon was much easier ). One lfs had one for 59.99 (the 25 foot). Big Al's sells the same one for 21.00, coming up to around 28 including shipping, more than half the price. Do people actually pay almost 60.00 for one of those? I couldn't believe it when I saw it. The same place also sold penguin biowheels that pump I think 100 gph for 40 dollars. I go there because they take good care of the fish, but I can't bring myself to buy anything else there, it is ridiculously overpriced.