Why is my RODI such high ppm?

[Auqaman]

I was curious to how effective my rodi filtration system is so I bought a digital reader. My tap water reads 35ppm and my filtered water (before I add the salt) reads 17ppm. Shouldn’t it be zero? Should I add another filter?

 

[Matthew Dambra]

35 ppm tap water sounds amazing. Your unit should have no problem making 0 TDS. Have you changed your cartridges lately?

 

[Auqaman]

I changed the 4 on the left about 2 months ago. I’d hope to get a little more life out of them. I wonder if there’s a way to increase the back pressure to get better results

 

[Matthew Dambra]

Unless you've been making a ton of water they should last alot longer than 2 months especially with your low TDS to start.

 

[DriftN201]

I am skeptical that your tds meter is accurate. If tap water is really 35 your filter isn't doing much if it only gets to 17. I would think fresh carbon alone would bring it down to 17. BRS has a pretty good video on Youtube about rodi. It might be helpful.

 

[BlennyTime]

Go buy some distilled water from the grocery store. If it tests higher than 1, your meter is probably busted.

 

[Auqaman]

It is a second hand meter. I’ll have to check the accuracy

 

[Auqaman]

Just checked it with distilled water and it’s reading zero. Going to the lfs for new filters now. Hopefully that’ll solve the problem

 

[Biglew11]

What's your water pressure going into the ro housing?

What's the tds between the ro and the di stage?

How much water has been through the di stage, is it exausted?

It's not the pre filters on the left causing high tds. It may be a bad ro cartridge. Can't tell from the pic how the ro membrane is hooked up to the di stage.

Edit: you have 35ppm going into the unit and 17 ppm coming out of the di stage. Your ro portion should be close to 1ppm how old is the ro membrane?

 

[Auqaman]

Update - it was the sediment filter (first one on left). I replaced it and ppm went to 0. The filter is only 2 months old and I make approx 10 gallons per week. Guess I’ll be doing more frequent filter changes. Good lesson learned!!!

 

[Biglew11]

With 35ppm going into the system the sediment and carbon filters should last a year or more. It's not those filter making your tds high. Has the ro membrane ever been allowed to dry? If you have 17tds coming out of the di resin and it changes to 0 when you replace the sediment filters them the di resin is also used up. If you have 17 tds coming off the ro membrane and it goes to 0 when you change the sediment filters there's an issue with the ro membrane. With 35ppm going into the system the tds out of the ro should be close to 1ppm. The sediment filters don't really remove dissolved minerals from water, only solids.

What's your water pressure going into the ro housing?

What's the tds between the ro and the di stage?

How much water has been through the di stage, is it exausted?

It's not the pre filters on the left causing high tds. It may be a bad ro cartridge. Can't tell from the pic how the ro membrane is hooked up to the di stage.

Edit: you have 35ppm going into the unit and 17 ppm coming out of the di stage. Your ro portion should be close to 1ppm how old is the ro membrane?

The water going into my system is 145ppm. I make about 160 gallons per month and go about a year between filter changes.

 

[Auqaman]

Not sure how to explain it. When I tested the water and got a reading of 17ppm I was sampling the water in my ato tank. So maybe there was some sediment in the tank that gave a false reading. Either way, this is definitely high on my radar now

 

[Biglew11]

Run the ro water into a clean glass and test that water.

If your getting 17ppm tds out of the di resin the the di resin is used up and needs to be replaced.

Also with 35ppm going into the system if you get 17ppm out of just the ro stage then the ro membrane has about a 48 percent rejection rate. It should be between 95 and 98 percent.

it is not the sediment filters causing higher tds. Look at the ro membrane and the di resin!

 

[Biglew11]

Update - it was the sediment filter (first one on left). I replaced it and ppm went to 0. The filter is only 2 months old and I make approx 10 gallons per week. Guess I’ll be doing more frequent filter changes. Good lesson learned!!!

Did you check the tds coming out of the di stage before you replaced the sediment filter?

you need to check the water coming out of the unit not in the ato resivior.

I get a year making 40 gallons a week with 145tds going in. If you start changing those filters every other month you're just wasting money.

 

[WvAquatics]

I have 350tds going in and after a flush and I start water my ro filters to 5tds so I would think somewhere something is off. Great suggestions above just chummed in how low my ro makes high tds

 

[Auqaman]

Yea sorry, definitely think I took a false reading. I scooped water out of my ato tank and not directly from the source. I don’t believe I needed the new filter (but doesn’t hurt anyway). Thanks for all the suggestions!!

 

[Opus]

Update - it was the sediment filter (first one on left). I replaced it and ppm went to 0. The filter is only 2 months old and I make approx 10 gallons per week. Guess I’ll be doing more frequent filter changes. Good lesson learned!!!

The sediment and carbon filters do not lower tds. The ro membrane is what does most of the work, with the di finishing off what the ro membrane doesn't remove. The sediment and carbon filters are just there to protect the ro membrane. More than likely you just had things accumulated in your top off tank. To get a good reading you need to turn on your ro unit and let it run for a few minutes and then take a reading of the water before the di. This tells you how well your ro membrane is performing. Of course after the di should be zero. My tap is around 450 and I get a reading of 4 after the ro membrane. With your tap water at 35, you should be getting a reading of 1 or less out of the ro membrane. This means your di should make over 4000 gallons of zero tds water.

 

[Tamberav]

Yea sorry, definitely think I took a false reading. I scooped water out of my ato tank and not directly from the source. I don’t believe I needed the new filter (but doesn’t hurt anyway). Thanks for all the suggestions!!

Was going to suggest this was the problem when you posted. I pour my RODI into a very clean glass to test

 

[Biglew11]

i'd recomend one these tds meters
https://www.bulkreefsupply.com/triple-inline-tds-meter-trm-1-hm-digital.html
you can put one probe on the source line, you can put the second one between the ro and the di stage, and the third right after the di stage. you can slide the switch to monitor exactly what the systems health is. one of the best upgrades i did.