Help needed with RODI (Vertex Puratek deluxe 200)

DanielBird

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Hi there!

I am struggling with my RODI. I'm seeing high TDS and nothing I've tried so far has helped. I'd appreciate any guidance. I've been throwing money at this problem and not really getting anywhere.

For the last 10 months I've been using a new Vertex Puratek RODI machine. I made roughly 40gallons a week of purified water and I was generally able to hit 0 TDS. About every 6 to 8 weeks the TDS would start to creep up and I would change the DI resin and get it back down to 0 TDS.

Two months ago the TDS started to creep up a complete change of the DI resin didn't help. I completely changed the sediment filter, carbon filter, and RO membranes but I was still seeing ~45 TDS after the DI stage. I added an extra carbon stage and an extra DI stage and I am able to hit 2 to 3 TDS at best after that second DI stage.

I've made sure that both the DI stages are very full with DI resin to avoid channelling. I've made sure the water reaches the top of the DI stage canisters (as I read this might help somehow). And earlier on I cleaned out the flow restrictor as I was seeing very little rejection water (this was before changing the RO membranes).

Here is a break down of the TDS:

My tap water: 450 TDS
After the Vertex Pentair RO membranes (which are rated for 98% rejection): ~45 TDS
After the first DI resin stage: ~45 TDS
After the second RI resin stage: 2-3 TDS

The pressure gauge on the machine reads about 40 PSI, which I realise is on the low side but I've never had higher PSI than this (and managed to get 0 TDS without problems).

I live in Denmark, where my impression is that water quality pretty good. Almost all of the water is groundwater. I've wondered whether I've been unnecessarily agonising over achieving 0 TDS when it is not necessary. Below is a screen shot of a water analysis from a local water plant. It certainly doesn't cover everything but it is the best I could find.

I am leaning towards concluding that my tap water TDS has increased as the most likely cause of these issues but unfortunately I don't have measurements from earlier on to confirm this. Still, that doesn't explain why I am seeing 90% rejection rates with brand new RO membrane rated for 98% rejection.

Any advice or recommendations would be greatly appreciated.
Daniel

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DanielBird

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UPDATE

In checking all the TDS values I noticed that it was odd that the first stage of the DI didn't seem to be doing anything to the TDS. Having very recently changed the DI I thought that it wouldn't need changing. But I gave it a go completely changing the DI in the second to last filter.

If anyone stumbles on this feed after struggling with their own RODI this is what I think happened:

The waste line got stuck and this somehow spoiled the RO membranes.
I changed the DI, carbon and sediment filters and this did nothing because the membranes were the issue.
I changed the RO membranes but there was still a problem with the TDS.
This was because in the short period between changing the DI and changing the membranes, the new DI got used up very quickly by the high TDS coming out of the old RO membranes.
Changing the DI for a second time fixed this.

My lesson from this experience - by a TDS meter and get to know the TDS values at all the key stages of filtration. Before, I just new the end result and I was trying to solve this problem blindly.

Daniel
 

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