RO unit: DI resin depletes quickly

[Mr31415]

I just got a new non-branded 5 stage RO/DI unit (see thread here 5 stage generic RO/DI unit - valve and drain question).

I have made 60 gallon of water. My DI resin cartridge is 90% depleted based on the colour change in the resin beads. The RO unit is connected to the outlet of my water softener. TDS post water softener is about 350ppm. I know Na+ is tougher on the RO membrane than Mg++ and Na++ - so this will be a factor. But I have never seen DI resin deplete so quickly. Is something else perhaps amiss?

 

[kharmaguru]

I just got a new non-branded 5 stage RO/DI unit (see thread here 5 stage generic RO/DI unit - valve and drain question).

I have made 60 gallon of water. My DI resin cartridge is 90% depleted based on the colour change in the resin beads. The RO unit is connected to the outlet of my water softener. TDS post water softener is about 350ppm. I know Na+ is tougher on the RO membrane than Mg++ and Na++ - so this will be a factor. But I have never seen DI resin deplete so quickly. Is something else perhaps amiss?

If you are on a well it's likely high co2 in the water. Colour indicator is not very reliable, the anion and cation beads rearrange themselves into layers and this can look like colour change when it isn't. It's best to measure with a TDS meter preferable an dual inline meter.

I know Na+ is tougher on the RO membrane than Mg++ and Na++

I've always believed the exact opposite. Installing after the softener is the best option and also how mine is connected.

 

[griss]

As Sean mentioned ^ are you on a well? If not, there’s a possibility the issue is TDS creep. Since your RODI doesn’t have an in-line TDS meter that will be hard to determine.

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In the past, I simply had my RODI connected directly to a float valve in the sump. And I was going through DI like crazy. That’s when I researched and learned about TDS creep.

Basically, when your unit shuts off and sits for a bit, the TDS “creeps” back out of the RO membrane. When you start the unit up again, this high TDS water in the RO housing shoots into your DI canister and depletes it quickly.

I no longer have the RODI connected to the sump and instead have it going to a Brute container.

When I need to make water, I open a bypass between the RO membrane and DI, and let it flush for a few minutes until the TDS coming out of the membrane drops. Sometimes the TDS on my meter is as high as the 50s depending on how long the system sat unused.

Some companies make a bypass system but, I had the parts so I just made it myself.

 

[polywise]

I'm on a well, and had high depletion rate of DI resin too.

I put an open topped garbage can with air stone post RO to degas the CO2 .. then used a dosing pump from that garbage can to run it through DI canister for ATO or makeup water.

I run this cycle:
Run the RO system with float control to fill the garbage can- then turn off the RO unit until garbage can is just about emptied... then turn off the dosing pump for a day to allow the refill of RO water and time to degas. then turn the dosing pump on to DI again for ATO
Has made a huge difference for me

Jim C

 

[michealprater]

I started using cation, anion and mixed bed resins and it fixed my issues.

 

[griss]

I started using cation, anion and mixed bed resins and it fixed my issues.

I do that as well, in addition to flushing the membrane housing before producing water. Those two things have greatly decreased how quickly my resin expires.

My RODI is setup as follows:
Micron Cartridge
Carbon Block
Chloramine Cartridge
RO Membrane
Cation
Anion
Mixed Bed

 

[Mr31415]

I am not on a well - this is standard city water, albeit a bit hard (TDS is about 350ppm before the water softener).

 

[Mr31415]

Can I flush the RO membrane in the unit shown in the link in my first post? I do not see a valve for flushing it...

 

[griss]

I am not on a well - this is standard city water, albeit a bit hard (TDS is about 350ppm before the water softener).

Also, contact your water company to find out if they use Chloramines to treat the water, if they do you'll want to add a Chloramine Cartridge after your carbon block and before the RO membrane. Chloramines can cause damage to the membrane causing it to be less effective. This would require a modification to your system.

 

[griss]

Can I flush the RO membrane in the unit shown in the link in my first post? I do not see a valve for flushing it...

Again, you'd need to make a modification to your system. You can either make your own bypass (to waste) between the membrane and DI with a "T" fitting and an inline Ball Valve or you could purchase a TDS Creep Bypass kit and install that.

 

[griss]

Another thought, what is your pressure in the RODI unit? Lower presser across the membrane causes it to be less effective at removing TDS. I had to add a booster pump to my system to make it more efficient.

ETA - it looks like your system does not have a pressure gauge on it.

 

[Mr31415]

Nope it does not have a pressure gauge but I do know that the pressure is relatively low in my house. I guess I have a couple of things I can look at:

1. Booster pump
2. CO2 removal

I will try and find out about Chloramines and try and measure the pressure.

 

[griss]

Before buying a booster pump, you might want to try installing a pressure gauge first. These are relatively inexpensive ($10-20 USD) compared to a booster pump kit at around $180 USD. No sense in paying for a booster pump kit if your pressure is already good

Here's a good video on how to install the pressure gauge.

 

[laverda]

You can also test for Co2 by puting some from the line feeding you DI into a cup and measuring the PH. Then aerate it for 30 minutes or so and measure the PH again. If the PH is significantly higher, Co2 is at least part of the problem.

 

[Mr31415]

I got a response back from my water utility:

In regards to your question about chloramines the answer is no. We use 16% Sodium Hypochlorite for disinfection at the Water Treatment Plant.

 

[griss]

That's good, you don't have to use Chloramine cartridges. Since you're not on a well, that should pretty much rule out CO2 from what I understand. So, I'm guessing it's either TDS Creep, low pressure across the membrane or a combination of the two.

 

[laverda]

I am not on a well, but have issues with Co2. Some municapilaties use well water. In my case the city uses well water in the dryer summer months.

 

[griss]

I am not on a well, but have issues with Co2. Some municapilaties use well water. In my case the city uses well water in the dryer summer months.

Interesting, I didn't know some municipalities did that. I guess living at the junction of the Missouri and Mississippi Rivers, I assumed they all used river or lake water. You know what happens when you assume

 

[laverda]

I am in southern Ca. I assumed our water came from northern Ca and the Colorado river. My Di lasted forever until I moved 12 miles and different city. Besides the initial TDS being a bit higher. I started going through DI much faster. It turns out during part of the year the city uses well water or a mix of well water.

 

[alton]

Like Kharmaguru said get an inline tds meter nd measure before the DI and after. If your ro water is 20 and above before your DI cartridge, your DI will be depleted quickly.