RO Issues


New member
I recently purchased a new Coralife PureFlo II RO 3 stage unit with the add on DI. When I first set up the system, the RO took our tap water down from 89ppm TDS to 26ppm, and the DI cleaned it up to 0ppm.

I made about 80 gallons of water, checking the TDS levels each 10 gallons or so. The levels remained unchanged for the entire 80 gallons. Today I was surprised to find that my DI was outputting 1ppm, and my RO unit was not cleaning the water at all (exiting at 89ppm). The unit had been ran for 9 days straight when this problem started.

I stopped the unit and flushed the RO membrane for 15 minutes as suggested in the manual. After flushing, the RO was outputting 13ppm TDS. Thinking the problem was solved, I started the unit back up. Three hours later, the RO was back up to 45ppm.

I know that our city uses chloramines rather than chlorine, and that this could potentially degrade the membrane over time if the carbon isn't sufficient to decompose the chloramines. But still, after 80 gallons? Has anyone else had a similar experience with RO units/know how to fix the problem? Thanks!


Got Reef
Premium Member
I wouldn't speculate on exactly what's wrong with your RO unit, but if your membrane is only taking your tap water from 89 to 26 then it definitely has a problem. A "normal" unit should drop 89 to no more than 5 or 6. Mine takes in water with 180 TDS and spits out water with 3 to 4 TDS. Going from 89 to 26 is just not a well functioning unit.

Your DI unit is probably wearing out so quickly because it's receiving water that's way too high in TDS.