I am looking into getting a Ro unit for my tanks. I am wondering exactly what one to get. I looked on ebay and found a couple different ones. I really would like to know if I really need a 6 stage Ro unit or if like a 4 or 2 stage ones will be just as good. If I do not need a 6 stage Ro unit, I would not buy it since in the long run it would cost more for replaces all the filters in it. Thanks.