Do a search on ebay for ro/di. You will find some good units there at great prices. I was using tap water for about the past 9 months or so and I just recently bought a ro/di unit off of ebay. It should be here within the next 3 days. I have heard that other than a skimmer and live rock these are one of the best investments you can have. I paid $130 for a 6 stage, 125g per day ro/di unit with extra filters. That includes the shipping and handling too. You might want to check one of these out.kobeSumo said:I've heard about R/O units, but I am at loss to figure out what size and brand I should get.