# Which RO filters to replace?



## darcyr (Jan 24, 2014)

I replaced my filters and resin but not the membrane 9 months ago and make 10 gallons a week. The membrane is 2 years old. I used to get 9ppm before DI resin and 0ppm after. Now Im getting 14ppm / 6ppm respectively. 

Do I only need to change the resin? All filters? When do you know the membrane needs to be changed?


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## Jmbret (Nov 6, 2010)

have you tried backflushing the membrane?


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## darcyr (Jan 24, 2014)

I have not tried that, I assume I just reverse the waterflow after the carbon and micron filters to the RO membrane and let it run a while?


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## Jmbret (Nov 6, 2010)

darcyr said:


> I have not tried that, I assume I just reverse the waterflow after the carbon and micron filters to the RO membrane and let it run a while?


 This --> 




Some argue this reduces the lifespan of the membrane but I have had more longevity from mine using this feature as needed. Whenever I see pressure drop, or TDS gets out of control, I backflush the membrane for 15 minutes and it is as good as new.


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## darcyr (Jan 24, 2014)

I have the melev's reef RO system and no flush kit, he also doesn't recommend it. I haven't seen reduced water production, just slowly rising ppm


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## goobafish (Jan 27, 2015)

If you aren't changing your other filters like clockwork every 6 months, its likely the membrane that needs replacement. Systems that allow you to flush are more forgiving, you can run some of the filters a little longer, and accidentally running hot water through the system won't force you to replace the membrane. With no flush, any damage or wear on the membrane is not repairable. The membrane can last many years if it goes undamaged, but to do this, the cheaper filters must be replaced very frequently.


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## noy (Nov 19, 2012)

A good working membrane will have a 95-97% rejection rate. So if your incoming water is at TSD=100 - it should return as 3-5. I would test your incoming TDS to see what your rate is - because the rise in your TDS going into your DI maybe just incoming water quality related.

You should get the colour changing DI resin so you can easily tell when your resin needs to be changed. Resin is fairly cheap - after 9 months i would just replace it to see what numbers you get.


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## goobafish (Jan 27, 2015)

Keep in mind that deionization's primary purpose for reef is the removal of chlorine and chloramine, which a TDS meter does not detect. Your DI resin should be either color changing, or also changed on a strict schedule, as the results of its processing cannot be tested.


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## duckhams (Oct 13, 2009)

noy said:


> A good working membrane will have a 95-97% rejection rate. So if your incoming water is at TSD=100 - it should return as 3-5. I would test your incoming TDS to see what your rate is - because the rise in your TDS going into your DI maybe just incoming water quality related.
> 
> You should get the colour changing DI resin so you can easily tell when your resin needs to be changed. Resin is fairly cheap - after 9 months i would just replace it to see what numbers you get.


+1 - Also, if your TDS is rising after the membrane, change the RO membrane is the first priority.


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## Lilphil26 (Sep 15, 2015)

Since we are on the ro/di topic. I still have my Ro/di from about 10 years ago. If i replace my carbon, sediment and di resin, would it be safe to say the membrane would be ok? It might have had 500 gallons run through it since new. I think it's a 50 Gpd unit. 

Sorry for the hijack btw.
Brad


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## duckhams (Oct 13, 2009)

Lilphil26 said:


> Since we are on the ro/di topic. I still have my Ro/di from about 10 years ago. If i replace my carbon, sediment and di resin, would it be safe to say the membrane would be ok? It might have had 500 gallons run through it since new. I think it's a 50 Gpd unit.
> 
> Sorry for the hijack btw.
> Brad


PM Sent.


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## darcyr (Jan 24, 2014)

I just replaced the prefilters and DI resin only and am getting the following TDS readings:

Tap 134
After prefilters 130
After RO membrane 10
After DI 0

I'm surprised the prefilters don't remove more but I'm back to making 0 tds water so I'm happy. Thanks for all the advice, I will change filters every 6 months from now on.


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## duckhams (Oct 13, 2009)

darcyr said:


> I just replaced the prefilters and DI resin only and am getting the following TDS readings:
> 
> Tap 134
> After prefilters 130
> ...


Id say your RO membrane needs replacing too. I get 147 from the faucet and 2ppm from the RO membrane before DI. Replacing the RO membrane will extend the life of the DI resin too.


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