ro/di acceptable ppm reading


New member
when using your ro/di to top off what tds reading shoul it have inorder for it to be safe for reef and fish. I just had a reading of 12ppm , i use to get 0 out of it , but is it safe ?


New member
You really want 0 all the time. If you keep using it for long, the TDS will keep going up and you may get an algae bloom.


New member
Do you have a reading before and after the DI stage. You might just need to change the DI resin.


In Memoriam
On my RO/DI 4 stage unit I run a 5 micron prefilter and a AC whole house filter then the 4 stage, with a second DI HS, I just got a TDS meter in and out probes. I have found when you first start making water the readings on the out let were running 27. 387 in, after 30 minutes the out let was down to 2, a RO membrane takes some time/ water flow to be totally efficient, that is why allot of people with auto top offs have problems, it is only adding a gallon or 2 and then shuts off, but the RO is not working to full capacity yet as far as removing TDS.


Premium Member
depending on your Pre RO readings, you post RO usually hits between 6 and 12ppm (there is a definite difference in RO membranes)

Most DI units will hold about 3000p and are close to 100% efficient until saturated. At which point the unit needs new DI media.

My Pre RO reads 175ppm / post RO is 6 /Post DI 0