Cannot get 0 TDS values

[Koty]

My RODI basic standard system is working well. The water here is hard and dirty, but the RODI gets 90-95% of the TDS off. The problem is that I have two resin columns next to each other with blue-to-brown color-changing resin. Both columns are transparent, and after about three weeks, the bottom 1/5th of them is brown, and the rest is blue as expected. Still, I get TDS values of about 60. Yesterday, I replaced all three probes with a new set (1. pre-RODI 500-700, 2. post-RODI 60-30, 3. same as 2). And got the same value of 60.
Finally, I do pack the columns very tightly to prevent channeling. Any ideas?
My auto top-off works for 5 minutes every 12 hours to prevent the system from exhausting.

This is the brand I use:

 

[Fishy888]

My RODI basic standard system is working well. The water here is hard and dirty, but the RODI gets 90-95% of the TDS off. The problem is that I have two resin columns next to each other with blue-to-brown color-changing resin. Both columns are transparent, and after about three weeks, the bottom 1/5th of them is brown, and the rest is blue as expected. Still, I get TDS values of about 60. Yesterday, I replaced all three probes with a new set (1. pre-RODI 500-700, 2. post-RODI 60-30, 3. same as 2). And got the same value of 60.
Finally, I do pack the columns very tightly to prevent channeling. Any ideas?
My auto top-off works for 5 minutes every 12 hours to prevent the system from exhausting.

This is the brand I use:

Have you tried replacing the RO membrane? I was also getting values like that too, until I replaced my membrane. Do you have a TDS meter after the RO membrane but before the DI resin?

If you have a BRS RO/DI unit check to make sure your DI resins are installed right side up in each canister. I was getting the same readings after the RO membrane as I got after the DI resin. It turned out the cartridge was upside down.

 

[Kmst80]

How long have the membranes been running? What are you running?
Due to your water beeing very dirty how often to you change sediment filter?
I run sediment, carbon, carbon, ro memrane, di,di.
The sediment and carbon staged are important or you wear out the ro membrane pretty fast.
When we had the floods here our input tds was around 400 and i got out 5 at the end, normally it's around the 200 and i get 1 or 2.

 

[Aquariumaddictuk]

My RODI basic standard system is working well. The water here is hard and dirty, but the RODI gets 90-95% of the TDS off. The problem is that I have two resin columns next to each other with blue-to-brown color-changing resin. Both columns are transparent, and after about three weeks, the bottom 1/5th of them is brown, and the rest is blue as expected. Still, I get TDS values of about 60. Yesterday, I replaced all three probes with a new set (1. pre-RODI 500-700, 2. post-RODI 60-30, 3. same as 2). And got the same value of 60.
Finally, I do pack the columns very tightly to prevent channeling. Any ideas?
My auto top-off works for 5 minutes every 12 hours to prevent the system from exhausting.

This is the brand I use:

Is the resin tightly packed?it sounds as if water is bypassing some of it if only bottom is changing colour
Membrane replacement may well be required but packing resing tightly is vital also

 

[Koty]

I live in Israel. Water are very hard. I have sediment, carbon, carbon, rodi, resin, redin. I test before RO, after RO, and after the two resin columns. The RO seem to filter 90-95% so I guess it nerrows down to the resin stageI have an "electrolite scale remover" for the entire home inlet. Not sure how it works, somthing to do with neutralizing ion charges. Is it the csuse?

 

[Koty]

Membrane and all prefilters are about 6 mo thes old.
I do not do water changes so it is only top off.

 

[Aquariumaddictuk]

If your only using for top off/ATO the membrane should be fine.i change membrane every 6 months but I keep two large discus tanks also so I need a LOT of water for large changes several times a week.id say check resin first.if necessary with that high TDs you could consider a second membrane in sequence though as it shouldn't be that high before resin

 

[Kmst80]

I agree with above post tds shouldn't be as high as yours after ro memrane, i would start with sediment and carbon filters since these are not as expensive as the ro memrane. There are different grades in sediment and carbon filters too. If that doesn't change the tds after the membrane then i would replace ro next. With water as dirty as yours i would change Sediment and carbon every half year at least coz they protect your ro membrane.

 

[KStatefan]

Is is possible that it is plumbed incorrectly?

 

[Koty]

Is is possible that it is plumbed incorrectly?

Nope
Will replace zediment + 2 x carbon ans see how it goes

 

[Stephen8169301]

If that’s the ro buddy off Amazon you gotta let the water slowly very slowly go through

 

[Randy Holmes-Farley Verified Community Expert]

Do you know that the meter reads 0 ppm TDS in air? Maybe it is not working.

 

[Koty]

Replaced the probes yesterday and the three pre filters (scc). I buy the resin and pack the columns myself

 

[Muffin87]

Your Rodi membrane seems terribly inefficient.
Do you have a booster pump to achieve the pressure needed by the membrane?
You should aim to get at least 25 TDS from the water leaving the membrane.

Get a decent meter, two possibly.

 

[Koty]

After replacing the pre filters i seem to get 95% efficiency. No booster but pressure from the system is about 90 psi. I think that dirty ptefilters may reduce the effective pressure on the ro membrane. Does this sound logical?

 

[Kmst80]

What is tds after membrane now? If your sediment filter is dirty it will reduce flow, but depending on density of your pre filtration it'll reduce flow the denser the filters are

 

[rhitee93]

I've been going through some RO/DI issues, so I have some numbers fresh in mind as another data point for you:

My tap water reads close to 400TDS on most days. Generally, after my sediment, carbon block and RO membrane stage I get a reading around 12 before the water goes into my DI stages. My DI stages easily take that to 0.

 

[Muffin87]

After replacing the pre filters i seem to get 95% efficiency. No booster but pressure from the system is about 90 psi. I think that dirty ptefilters may reduce the effective pressure on the ro membrane. Does this sound logical?

You should get one of those washable prefilters, they are about 20 micron.

90 PSI into the dirty filters or into the RO membrane?

 

[workhz]

Wouldn’t only running for 5 mins (without flushing anything) cause high values?

Do you get 60 at the beginning of the process or end?

I’ve always been told that doing small batches vs a large batch exhausts DI resin quickly.

 

[Muffin87]

Wouldn’t only running for 5 mins (without flushing anything) cause high values?

Do you get 60 at the beginning of the process or end?

I’ve always been told that doing small batches vs a large batch exhausts DI resin quickly.

To avoid exhausting DI resin quickly you must simply put a bypass with a valve after the RO membrane.
This way, by closing the valve, you can prevent high TDS water from ever entering the DI cartridges.
By opening the valve, you can divert low TDS water into the DI cartridge, once the RO membrane has started producing water with the lowest TDS possible.