I recently purchased a ro unit and was wondering if the membrane was working properly. So I've purchased a dual inline tds monitor which is suppose to tell me if the membrane is functioning effectively. My question is what should the the output or product water tds be for me to safely use for my reef tank? From what I understand if the feedwater is 200ppm then your product water should be 10-20ppm, or 90-95% rejection rate. But I am very confused by a statement the tds company makes about salt water aquarium use of ro water: "A constant level of minerals in the water is necessary for aquatic life. Changes in the amounts of dissolved solids can be harmful because the density of total dissolved solids determines the flow of water in and out of an organism’s cells. Concentrations that are too high or too low may limit the growth and may lead to the death of many fish or reefs. A level of 400ppm or less is recommended for most freshwater fish although many softwater fish demand a significantly lower level. Conversely, saltwater fish require a very high level of anywhere from 5000 to 50,000 ppm. Total Dissolved Solids are also important for proper osmotic regulation, which is the relationship of water versus dissolved solids in the cells and the external environment. The greater the amount of solids in the water versus the solids in the tissue of the fish will result in a fluid loss via the gills." If this is the case using ro water with a tds of 10-20 ppm would be toxic!?!?! Someone please help me understand this!!!!