Mystery DI Killer

I have no answers, so I came here.

We’ve got 4 RO/DI units, but one of them is killing the DI within 2-3 hours of use. That one is the Tucker RO/DI cart. We recently replaced the membranes in two of our units with the Axeon HF5. The prefilter is new. The ro membrane is removing approximently 92-93% of the tds from the tap, which usually ranges 350-450. So the DI has had water coming into it that has been between 30-45 tds. Works for just a couple hours, the the tds starts getting worse out of the DI, then it was going IN the DI housing. Starts creaping higher and higher till we can’t clean windows anymore. We’ve trying nuclear grade resin from a certain vendor, same result, some older resin we had from WCR, same result, brand new resin from WCR, same result.

The membrane seems to be working great in the tucker machine and in our wash it pro. I think we started having the issue before we swapped membranes, and it was the reason we changed the membrane.

Similarly, the DI in the Wash-it-pro has been doing it’s job just fine as well.

We’ve also swapped the DI canister itself, with a new canister

We are all scratching our heads, and it’s driving us up a wall and it continues to try to ruin our work days.

Does anyone have any clue to what’s going on?

@Chris @RHG_Products @John @Alex @Infinity

It sounds like a problem I had where the DI canister was not seated properly in the housing.


That was my first thought, that only water with such high tds could kill di that quick. Some of the unfiltered water must be getting through to it.

I thought the tds coming into the DI should be much lower, 10-15 range.
Are you using a pump? if the psi is too high that can cause issues. under 100 psi on the RO is the max mine can handle without issues.

If your tap tds is around 175-200, Then you would get those numbers. But low pressure ro membranes don’t filter above around 95%, from what I’ve seen.

Ro membranes actually run MORE efficiently with more pressure. But no, I don’t have a pump connected.

There’s no possible way unfiltered water is sneeking around the ro and making its way to the di

That still doesn’t seem to explain why the tds is higher coming out of the di than going into it.

Idk then about the water getting around, but the tds coming out higher than going in is just a sign of bad di resin.

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I understand that, but no matter what brand/age of resin we put in there, it only lasts 2-2.5 hours max.

low psi is bad for pure water but too high is not better. optimal 60 psi range, below 40 is bad.

When you say pure water, do you mean for the membrane, the di tank or for output?
Each membrane is rated for a certain psi.

The Axeon hf5 might be the best ultra low pressure membrane on the market. It’s rated for as low as 80 psi, but can handle up to 400. It runs more efficiently with MORE pressure.

On the other hand, you can run di tanks with too much pressure. Too much pressure may cause tunnels in the resin, and too high of gpm can cause the water to move through the tank/canister before it has enough time to “marinate” in the resin and “shed” the minerals.

You’ve ran the same water source thru all of your set ups?

Because the first thing that comes to mind for me is chlorine? That sounds about the range of water with chlorine in it.

Hey what’s up Tori , how you been doing ? Are you still commuting from tj? I saw a report on the line taking 8-10hours to cross

Chlorine should all be handled by the new prefilter. Anything left would be dealt with by the RO membrane.
Different water sources, but ones we’ve used many times before

why are you using di at all. ro should bring 175 tds down to 5-10 which is fine. i have not used di in 3 years or maybe it’s 4.

Our tds averages 350-400 from the tap

and what is it out of the ro?

30-40 tds

unless your di tank is teeny tiny or a huge lump of mud in it this is indeed a mystery.