Why not just DI water?

[Mr. Microscope]

So, I recently read a post saying that one can use RO, RO/DI, but not just DI water. I started my tank yesterday with LR&LS, and used only DI. Actually, I used ddH2O. I work in a lab and have access to this super pure water. Is it missing something that I need? Should I add RO to the mix?

[Mr. Fosi]

You aren't missing anything because you have access to quality DI water, unlike most people. I use DI myself, for the same reason.

 

Most people don't use DI alone because their tapwater will too quickly exhaust the DI resin. Better to put an RO membrane before the resin and save yourself the money.

[seabass]

^agreed

 

There is a rechargeable DI only option for hobbyists, which you don't need to run an RO membrane prefilter. However, I would still run a sediment and carbon prefilter.

[vresor]

DI alone produces the same finished water quality as RO pre-treatment for DI resin canisters. The only difference is in the life of the deionization exchange resin. With reverse osmosis membranes taking out 85-95% of the ions (like phosphate, calcium, bicarbonate, iron, etc.), there is less for the DI resin to remove.

 

The real question is whether or not RO can produce good enough water without polishing it with DI media? That depends on what you pump into the RO membrane. My guess is that phosphate, the real offender in municipal water supplies, would be reduced to less than 0.5 ppm in most applications since PO4 is relatively easy for RO membranes to remove. Whether or not the biofiltration in your fuge could handle that is another good question.

[Drew220]

I use DI only and get mine from my lab. I figure if it's pure enough to use as blanks then it will be fine for my tank. Of course the ion-exchange canisters at work take up a whole room and has UV sterilization unlike the small units you use in the house.