Unless you want to go back to having new water sit overnight.I actually still do that with some of my smaller tanks....My answer to the question though would have to be gravel.I have a few buckets full sitting around that I may never use again because I no longer like the color.geronimo69;4784239; said:I'd have to say dechloronator (prime). It gets expensive(buying so much), but I guess isn't a waste either!