RO/DI question (membrane)

cloak

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Just a little background my 4 stage BRS RO/DI filter has got to be at least 3 years old. All 3 filters were replaced maybe 3 months ago. (DI resin, carbon block, sediment filter) I usually only make about 15 gallons every 3 weeks or so. The DI resin I have changes color when it becomes exhausted and it's still looks brand new. Today while I was making water I checked the TDS and it was at 7. Assuming the unit is working properly and the filters are relatively new, could the high TDS be due to an old membrane? Thanks. :)
 
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PBar

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Hello,
If I understand correctly, it is very likely linked to the RO membrane.
Just to be sure, when was the last time you changed the RO membrane? 3 years?
Again, if so… I would definitely order a new one... besides, it does not worth the risk.

In my case, I change it at least once year independent of amount of the water produced, just to avoid headaches. Mostly because, other variables play on it, such storage, temperature, dry inside by accident…

Cheers And good luck!
 

redfishbluefish

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I don't think it's the membrane. I make 70 - 100 gallons per month and still have the same membrane I had 15 or so years ago. I do back-flush the membrane and assume this helps in keeping it clean. Oh, and I'm getting 2 TDS before DI....so it's still working.

What is your raw water TDS? With a quality membrane, you should be getting a minimum of 98% reduction in TDS. Another consideration is water source.....are you city water or well?

The other consideration is how you use your unit and frequency of turning on and off. To get to the chase, every time your unit turns on, you get breakthrough TDS. Within a couple minutes, this is cleared and you're producing "good" water. The issue is that this initial high TDS will quickly eat up your DI resin. To eliminate this, run the first couple minture of water to waste, and then start running through your DI resin. For me, I actually wait 12 minutes and then flip a valve to start to collect good water. I use a three-way valve available at BRS.

BRS Three Way Valve.jpg
 

Townsaquaria

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Change out your sediment filter and carbon blocks and then check the TDS. If it's still high, change the membrane. If that doesn't do it, change the DI filter. Then if still high, your source water could be really high, you could have too low water pressure, or you're getting a false reading. Also make sure you're flushing the membrane after every use. Personally me I just change all the filters out at the same time. I just had 7 TDS reading and changed filters and I'm back to 0.
 

TexanCanuck

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@redfishbluefish has got the right idea.

Measure the TDS of your raw water inlet to the membrane and then the TDS of the output after the membrane

Then based on the temperature of the water, compare the actual rejection rate ([TDS in - TDS out]/TDS in) with the manufacturer's claimed rejection rate (example: I use SpectraPure's membrane which provides 99% rejection at 70 degrees)

If the calculated rate is relatively close to the recommended rate, then your membrane is fine.
 
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cloak

cloak

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The membrane has never been changed. So yes it's at least 3 years old.

The TDS of the tap water is currently 222, but this seems to vary. I've seen it as low as 28 before. (usually in the summer)

This is city water, not well water.

When I do use the unit I let it run for about 5 minutes before I start filling up a bucket.

The unit is stored in my room, away from the elements.

Thanks for the replies. :)
 

dhnguyen

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when in doubt test the product out of the RO membrane and see. But I would suspect that yes your RO membrane needs to be replaced. They usually last anywhere from 2-4 years depending on incoming water TDS so 3 years seems up there already.
 
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cloak

cloak

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Thank you all for the replies. :)

I ordered a new membrane as well as a carbon block, sediment filter & DI resin. Will replace the membrane first and then report back. Thanks again.
 

LeftyReefer

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The membrane has never been changed. So yes it's at least 3 years old.

The TDS of the tap water is currently 222, but this seems to vary. I've seen it as low as 28 before. (usually in the summer)

This is city water, not well water.

When I do use the unit I let it run for about 5 minutes before I start filling up a bucket.

The unit is stored in my room, away from the elements.

Thanks for the replies. :)

When you do this, are you running the water through your RO membrane and DI resin? If so, that isn't what you want to do... you want to install a diverter between the RO and the DI resin. That allows you to flush your RO membrane of high TDS water, and send it right down the drain, instead of sending that high TDS water through your DI resin, which will exhaust them faster.

You should install a diverter valve like redfishbluefish posted above. Install it between your membrane and DI. Then you can avoid sending any high TDS water through your DI resin.
 

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