I agree. The distilled water is probably the way to go. Be sure to test for both pH and hardness as you do this though. If you lower the buffering capacity of the water too much, it can very quickly go acidic. pH is relatively easy to raise...not so easy to lower. Once you get the tank to where you want it, mix distilled with your tap water until you find the right ratio. Then you can use that for all your water changes.