DI unit sizes

[Crepe]

So this is really confusing...I'm finally setting up my RO system again and this time around I'm going to replace the micron filter with a DI cartridge. However my cartridges are 9 3/4" while all the DI cartridges on Marine depot and bulkreefsupply and other places are 10"....More confusingly I googled 9 3/4" DI cartridge and got something titled: "10" DI Cartridge" and under the specs it says 9 3/4".

Is it that 10" cartridges are all 9 3/4"? Also my RO system is a Five stage unit....do I really need that last water polishing stage? It's supposed to remove taste from it or whatever but from what I gather after just the prefilters, RO and DI TDS will hit 0.

 

[neilanh]

I would keep the micron filter and add the DI on at the end. The micron filter will help mechanically filter out particles and keep your membrane cleaner. Also this way it doesn't matter what size it is, just plumb it in after the pure water output of the RO filter and you're all set.

No, you don't need that final stage. IIRC it's just a carbon stage. I tossed mine and added a 2nd DI stage.

 

[Crepe]

So I'm guessing the DI unit doesn't need that much pressure? That was the plan but then I thought that I didn't really want to deal with cutting and remeasuring everything...So just plumb it in between the RO outlet and reservoir(pressurized) or reservoir and my filling valve(part that goes into my trashcan)?

 

[neilanh]

either way would work actually. It doesn't need much pressure at all, you just want the water to pass through it.

 

[Crepe]

Alright thanks, I guess I'll add the DI to my shopping list later...RO will have to cut it for now. It's for my FW tank anyways.

 

[Kurt_Nelson]

I would keep the micron filter and add the DI on at the end. The micron filter will help mechanically filter out particles and keep your membrane cleaner. Also this way it doesn't matter what size it is, just plumb it in after the pure water output of the RO filter and you're all set.
...

In addition, if you plumbed the DI resin BEFORE the RO membrane, the DI resin would be no good after about 20 gallons! DI resin will remove impurities in the water just like the RO membrane will.

The reason you add DI to an RO system is because the RO doesn't get rid of 100% of the impurities - most will get around 95% of the "bad stuff" out of the water. The DI resin will then get the rest of the junk out of the water and not get used up so quick because it's dealing with much less "bad stuff."

So say you have 100 ppm TDS tap water, the RO output will be about 5 ppm, and the output from the DI resin would be 0.0 ppm.