Hi, I have had a saltwater tank for almost a year now and am looking into getting an
RO/DI unit. It is rather troublesome to get water from my "local" fish store, which is about 30 to 45 minutes away

. I don't know much (if at all anything) about an
RO/DI unit, other than the fact that it purifies water. I was wondering what I need to operate a unit such as this, where to find a descent priced unit, and how it works. I have noticed this thread on the
Talking Reef forums:
Choosing an RO Unit but it does not answer the questions I need answered. Also, what is a
TDS meter? It appears that this would be helpful and would be a part of the answer to my first question. As a note, I have a 55 gallon tank (without a
sump). Any and all help on this topic would be much appreciated. Thank you in advance.