RO, DI

[ClownieTang]

Do I need a Deionizer for a reef aquarium? without it, is just using reverse osmosis water the same as using a drinking water filter? My LFS sells RO SW, that I buy every 2 weeks for a water change. I refill my tank every day with regular filtered water from the sink (because of evaporation), that goes through a drinking water filter system. If I buy RO freshwater from my LFS to refill the evaporated water, will it be the same as a drinking water filter because there is no Deionizer?

[Reefing Madness]

Do I need a Deionizer for a reef aquarium? without it, is just using reverse osmosis water the same as using a drinking water filter? My LFS sells RO SW, that I buy every 2 weeks for a water change. I refill my tank every day with regular filtered water from the sink (because of evaporation), that goes through a drinking water filter system. If I buy RO freshwater from my LFS to refill the evaporated water, will it be the same as a drinking water filter because there is no Deionizer?

RO water is 98% pure water, RO/DI is 99.98% pure water. Don't know where your at, but drinking water here in AZ is pretty rough. It has metals, ammonia, chlorine. Your RO takes care of most of that, but not all. Most would tell you that for a Reef you definately want your TDS (total dissolved solids) to be 0, and you need the DI to accomplish that.
And, I have a drinking water filter on my fridge water line, that is by no means even close to a 4 stage RO system. You have to tell me what kinda filter your running for your drinking water, it may just be RO water, which is good, but phosphates still get through some of that. To know for sure buy a Inline TDS Meter to test your drinking water.