The friendliest place on the web for anyone with an interest in aquariums or fish keeping!
If you have answers, please help by responding to the unanswered posts.
tap water is not recommended. you dont need a ro/di unit, you can buy bottled water if you want to make if yourself, or go to the lfs and buy the water premade, its usually like $1-1.50 a gallon.
we've got a water treatment company (Like the Culligan man) here in town with a machine outside their offices that sells purified & drinking water @ $0.10 / gallon. We've been using purified water.
That RO/DI starts to look rather cheap over the long run. I did just buy 2 gallons of water though. I dumped it down the drain, refilled with RO/DI and made my kalk mix.