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ro water - is di needed ?


Well-Known Member
anewbie: I don't use a DI cartridge. I leave that unit empty. I don't need 0 µS water and feel that it is a waste of money since I would just be adding organics to it anyway. My water was good enough that for years I kept a breeding colony of cardinal tetras reproducing in it. I only change my micron & carbon filters when I see the intake pressure start to rise. Then I know the cartridges are clogging. This means once each year on average. The R/O membrane has never been changed in the 10+ years that I've used it. I'll know when it needs changing when the water conductivity rises above 40-50 µS.

The above is @Mike Wise post in another thread and i decided to stop thread crapping and open my own topic. Vaguely i thought the di stage was needed to remove kh; do i really need the di stage if the tds is low ?

I realize that from other threads Mike runs his water through peat bed which is removing some ion and colorado has softwater base water than i have here - mine is 120 tds (kh 3); so while not hard water it is still harder than colorado ( used to live in the boulder region and it is great esp if you enjoy the mountains).

I don't use the carbon block since i have two carbon pre-filters removing all chlorine; so that really just leaves the ro membrane and sentiment membrane if i can remove the di phase. I think the The tds is below 10 before the di stage - i think around 4ish if the gauge on the ro unit is accurate. I'm currently using around 500 gallons of ro water a week and soon it will be 800 as i move my aquariums to softer water - the aquarium with a. pucallpes has cupido added and i've been advise to give them softer water and there is a spare 240 downstairs i might put wild caught discus and gbr in.


Well-Known Member
Yes, the DI is not a must have. And the RO membrane already takes out 98% of GH (and thus KH), usually.

Mike Wise

Staff member
5 Year Member
Denver, Colorado, U.S.A.
Let us know what the conductivity is from your R/O unit without a DI cartridge. If it's below 50 µS/cm I personally wouldn't worry about using a DI unit. If you do feel that you need a DI cartridge then you might look into regenerating the media by yourself. It is possible but requires very caustic chemicals; not for amateur chemists.


Well-Known Member
The tds is below 10 so that would put the conductivity below 20; this is based on the in-line meter that came with the ro unit. What i'll do is not replace the di next time it wear out and get a more accurate reading but i think it will be around 15 for conductivity. My tap water is only 120 so not horribly hard.

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