Which RODI component to replace?

[adamf83]

Yesterday, my RODI system started to read 7ppm, rather than the usual 0ppm. This is the first time in just under a year since I’ve had the system. I’ve ordered a new carbon and sediment filters, a membrane and DI resin, but which is likely to be the one I need to replace?

I don’t produce a lot of water, maybe 100-125L every couple of weeks. The DI resin says it’s rated life is 1500GL which is around 5000L.

Is there an easy way to tell which one needs replace or an order to test in as I don’t want to change something unnecessarily?

If it helps, my tap water is 151ppm.

 

[Emptyness]

Since you have all the components - I would start small and change the sediment filter only. Then check the water.

You have made about 2000-2500L until now and since your DI resin is for 5000L, so I doubt that's the problem.

Of course, all depends on what exactly are those 7ppm and what exactly is the composition of your 151ppm tap water. But I doubt you can tell, so you can just do the "guess work" and change 1 thing then test the water. If no improvement - return the old component and change the next one - then test. If small improvement - leave the first replaced component and change the 2nd one too - maybe 2 of them are at their limits. Until you get 0 ppm again.

Note that you need to run the water for some time through the system and then test it. Usually 15-30mins. There should be manufacturer recommendation for each of the components.

 

[AZMSGT]

DI resin ratings are not accurate. It matters what the incoming water quality is. If that water is poor then your DI resin won’t last. Most DI resins have color change has yours changed color?

Does your TDS meter, read all three positions? Incoming, RO outgoing and DI outgoing? What position is it in. I made the mistake once of bumping the switch and was reading the RO out instead of the DI out. I changed resin and there was no change till I figured out my error. Just something to double check.

 

[adamf83]

Is 151pm poor? I think I’ve seen worse readings on other threads.

I don’t know if it changed colour, I don’t remember what it looked like when I started.

I only have a handheld TDS meter, I plan on getting an inline one at some point.

 

[AZMSGT]

The original color of DI resin is Dark blue, it turns tan/brown when spent. In some cases you will see a tan line moving from top to bottom. What can happen is the resin will turn back to blue after some time.

Your hand held TDS meter is probably more accurate than any inline version.

Disconnect the line that feeds your DI side and take a reading. If it reads high or close to your normal water then it’s likely your RO membrane. But considering the system is a year old it wouldn’t hurt to change everything.

After everything is changed, take baseline readings. This way in the future you can see if you get an increase in TDS you can troubleshoot the source easier.

 

[andrewkw]

If you're using a handheld meter you have to be absolutely certain you are using a 100% clean container to measure. This is a big reason why I prefer the inline.

That being said I typically change my sediment filter when either I notice decreased performance or I happen to see how brown it's got. I also change sediment filters on my house water system so it's somewhat easy to remember this, plus they are like $3. The carbon block I change probably every other or ever 3 sediment filters - still reading 0 TDS at this point. In almost any situation where the water isn't terrible you likely don't need to change all your filters at the same time. ie the sediment will clog first or you will burn through DI under certain situations which you don't appear to be in.

My DI I change either when I reach 1 TDS or at the start of the year. Looking at mine it has mostly changed colour but still producing 0 TDS. That being said I'm likely to change it in January just because I don't check the TDS meter every single time I make RO/DI.

The hardest one to figure out is when to change the membrane and it's physically hard to change too. For the filters though everyone's situation is different. If you are not burning through filters it may be best to just stick to a schedule.

 

[Emptyness]

Is 151pm poor? I think I’ve seen worse readings on other threads.

I don’t know if it changed colour, I don’t remember what it looked like when I started.

I only have a handheld TDS meter, I plan on getting an inline one at some point.

I have around 250 ppm tap water, so no, I don't think 151ppm is poor. The question is - what are those 151 (ie. what needs to be removed in order to get to that 0ppm RODI water)?

I am using a handheld TDS meter as well, don't have an inline one.

 

[Biglew11]

You need to be absolutely certain that the container your measuring in is absolutely clean. If your still reading 7tds after the di ressin then it is used up. Changing the other may decreas your tds some, but anything that still makes it through won't be stopped by the used up di ressin. If the di ressin is used up it will start leaching the stuff it has removed, starting with the one with the weakest bond (usually ammonia). Used up di ressin can actually increas the tds. You need to know the tds between ro and the di.

Disconnect the line between the ro stage and di stage and get a tds reading coming out of the ro stage. I get around 2 tds out with an input of around 145tds in.

 

[adamf83]

Turned out to be the sediment filter. I’m back to 0 TDS now, but an in-line meter is something I’m going to get to help identify this easier in the futrue.

Thanks all!

 

[Biglew11]

If changing your sediment filter brought you from 7tds to zero. Your di resin was still letting stuff pass. The sediment filter removes particles, not dissolved solids. The carbon block is the only one besides the ro that can influence tds. I suspect your container was dirty. Doesn't take much to influence tds in a small glass.

You still need to get a measurement of the tds between the ro membrane and the di stage.

The di resin is there to get you to zero tds. If your not at zero tds after the di resin, the di resin is still exuasted. It doesn't matter if changing the other filters got you to zero the di resin will not be doing its job.

Are you absolutely certain that the test container was clean in the first place.

 

[Snoopy 67]

You should rinse the carbon when replacing to remove the fines that can clog the membrane.
Do this by disconnecting the line from the carbon block to the membrane & let it run until clear.

 

[adamf83]

If changing your sediment filter brought you from 7tds to zero. Your di resin was still letting stuff pass. The sediment filter removes particles, not dissolved solids. The carbon block is the only one besides the ro that can influence tds. I suspect your container was dirty. Doesn't take much to influence tds in a small glass.

You still need to get a measurement of the tds between the ro membrane and the di stage.

The di resin is there to get you to zero tds. If your not at zero tds after the di resin, the di resin is still exuasted. It doesn't matter if changing the other filters got you to zero the di resin will not be doing its job.

Are you absolutely certain that the test container was clean in the first place.

Whilst it was a clean glass, I guess it’s possible it was the cause. In any case, I’ve replaced it now, so I’ll just have to keep an eye on it