What's everyone using for their water? RO or DI or ? I'm close to getting a nano tank and I'm wondering if DI water is OK, or is RO better? I think some folks use both from what I've seen in a reef forum. I'm planning on a fish plus live rock tank. I was thinking about starting up by getting a small DI unit to get the tank filled (34 gallon) - would that work or is an RO really needed? (Trying to keep the cost down too).