mag 18 on a 120 gallon manifold with 3 valves for UV and 2 reactors phos and carbon and extra valve for removing water or any other connection needed.40 gallon long sump, 4 chambers with the one on the right for rodi makeup water holding 8 gallons. all pipng leading to 7 inch filter sock and i drilled another hole on the sock holder for the uv return line. The makeup water chamber has a small pump connected to a timer which turns on for 15 minutes and a small valve controls how much water gets put back in 15 minutes i usually evap a gallon a day so i adjust the valve to allow that much water added in that time frame, if im off a little you can turn on the timer manually and just fill it to the max water level fill mark which i marked on the glass.