Benefits of adding a second DI filter?


Active member
I am looking to upgrade my 75gpd RO/DI unit to a 150 gpd unit. While I am at it I was considering adding a second DI unit to my setup. I believe I read somewhere that this is beneficial in extending the life of the DI resin. Can anyone confirm this or provide some insight for me?


If you add a second DI chamber you will have to change your resin half as much. It wont make it more efficient. If I had another chamber sitting around, I wouldnt make a second DI chamber, I would use it for a finer carbon block, that way less chlorine, chloramine gets to your ro and di, making those two last a longer.


New member
2 DI stages are preferable not to increase the lifespan of your DI resin. instead 2 stages allows you to fully exhaust every last bit of your resin.

Say you have a single DI stage with color-changing resin. When do you change the resin? Once it has completely changed color and fully exhausted? As more of the resin becomes exhausted, the contact time for the water passing through decreases. This can result in TDS numbers of the effluent (the water exiting the DI stage) to go up.

With 2 DI stages, even once the first stage is 100% exhausted, the water still has the contact time of a full canister, TDS stays at 0. At this point, you take DI stage 1 offline and replace the resin in it. Move the stage 2 canister to the first stage and the fresh DI resin goes in stage 2.

So the second stage doesn't increase the lifespan per say, it allows you to exhaust the resin fully without the risk of increasing the TDS of the effluent.