I have no access to better RO/DI water. I'm using the Aquarium Pharmaceuticals Tap unit. It's a one membrane filter which I now believe to be DI only. At one time I thought it was RO. It contains carbon on the bottom and what almost looks like Chemipure in the middle. Top and bottom have thick pads. The water flows first through the carbon, through the resin and then out. Is this RO or DI?