Like arnold said DO NOT start the tank on conditioned tap water. You will kick yourself later down the road. If you really don't want to use your r/o unit then go to wal-mart and get gallon jugs of distilled water. Not drinking water, distilled water. Before I got my r/o unit I used wal-mart water for everthing, top-off, water changes, and filling up the tank. Its like 50 or 60 cents a gallon. If I were you I would just bite the bullet and use your r/o unit save that money
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