Mugwump's Fish World

Jon and another member on the angelfish forum were posting responses to a discussion about RO/DI unit use.  Comments were made about bacterial growth in the DI canister and that it doesn't need to be used in a freshwater set up.

I have a RO/DI unit and well water here so no chlorine goes through any part of my RO/DI unit. I blend RO water with the well water to cut back on calcium deposits.  Pre-RO water goes through a house carbon sediment filter and a water softener.

So.....after "googling" way too much about bacteria in these units (freaking myself out then deciding I've survived over 60+ yrs in spite of a variety of bacteria in bio-film) I thought it would be best to ask here.  Can I run my RO/DI unit with the DI canister empty? There are "things" all connected to each other on the unit. I don't want to create a malfunction or leaks by trying to disconnect everything from the DI part. I thought maybe I could put another sediment or carbon block in there but am not sure if I can do that either.

Not having to use the RO part would be quite cost saving.  The resin gets exhausted quickly requiring replacement every 2-3 weeks!

...I don't see where another carbon block or sediment filter would any harm...the DI unit is normally mounted last, after the membrane....it's used to further reduce your TDS's..The R/O unit removes 95%+ of the TDS's already, DI uses resins to finish the job....if you pop a sediment filter in there it wouldn't do much but it can't hurt....and it's easier than wasting a carbon block...

I guess I could check the in/out TDS readings as water runs through the sediment filter that replaces the resin.  I will also see if the unit can be run with nothing in the DI canister.....just the water flowing through it.

I would go along with Mug. The DI part is not neccesary to function of the RO. It should run fine without it.
I my unit the DI is in front of the RO and would presumably take out ions that the RO would take out if the DI were not there to get it first.
On the other hand, If the RO membranes are exposed to and taking out the ions, the RO membrane may have a greater tendency to clog up with precipitates of those ions. So it might reduce membrane life, or your could flush out your membrane more often (if that is possible on your set-up).

Bacteria growing on stuff is not something I would worry too much about if you are not having some kind of problem that you know of. It is probably growing on anything not in chlorinated water. Also, if your system is set-up like mine RI before RO, and your RO membranes are intact (your getting good reduced conductivity water out), then any bacteria coming out of the RO machine would have to be from a source downstream of the RO membranes becasue the holes in the RO membrane that the water goes through are of a molecular size (much smaller than bacterial cells). I guess the bacteria could coat the membranes and clog it up but you would see that in a reduced output.

Bacteria growing on charcoal is not uncommon and I have some kind of algae growing in my DI cannister (which was clear to see it color). Its unlikely to be some terrible kind of bacteria. Zebrafish have at least 14,000 different species of bacteria in and on their bodies. most of them are either innocuous or beneficial to the fish. People have similar numbers. A mature biological filter would probably have at least several thousands of different species.

Well thanks for the info.  I certainly won't miss buying the resin nor changing it out.