Hi fellow reefers, I’m using a second hand madpetz 5 stage RO-DI system. Pressure gauge is not working. Tap water (75ppm) runs through stage 1 (rust & sediment filter) followed by stage 2 (granular activated carbon filter) then stage 3 (carbon block filter). Water ppm after 3 stage is (74ppm). After stage 4 (RO membrane), water (9ppm). Lastly after stage 5 (Resin) water (2ppm). Have bought this from a fellow Reefer, didn’t change any filters so far as I was told that by changing the resin it would be able to maintain 0 ppm water. Would require some advise if it is normal for water ppm after going through 3 stage filter to be only 1 ppm difference from tap water. Any idea if the pressure gauge can be replaced? Lastly, do u guys install a pump booster to rodi system? As I notice the water from the tap is quite strong, but as it comes out from the resin, the flow is really very slow compared to the tap. Staying in HDB .