RO Membrane rejection rate?

schigara

schigara

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Jan 2, 2005
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Memphis, Tn
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I am looking to get a new RO membrane and have been looking at the GE and DOW brands. How important is it to have the 98% rejection rate?

It looks like all the membranes I have looked at from 24-75gdp have a stabilized rejection rate of >98% and all the 100gpd membranes have a stabilized rejection rate of 90%.

Will this 8% difference help prolong the life of the DI cartridge?
 
I use the Spectrapure certified membranes. Guaranteed 98% 90GPD.

http://www.spectrapure.com/St_replac_p3.htm

It's a hard call. As it depends on your source water and how effective your carbon block is. 90% of a lower mineral laden water may not consume your DI as fast as 98% of some high mineral source.

We CAN say that your DI will last at least 8% longer and it could be substantially more than 8% longer with a 98 instead of a 90.
 
Thanks for the info kcress. After looking into DI cartridges and refillable resins, I realized it wasn't as big a deal as I thought is was. A DI cartridge at the LFS will run $38-46. I just bought 2 refillable cartridges already loaded with Nuclear grade, color changing resin for $36 total. I also bought an extra housing to make my RO/DI into a 5 stage and will run 2 DI's and also bought the Dow Filmtec 75gpd membrane for $45.
 
I know a lot of people make a big deal out of that rejection rate difference, but our RO/DI has a 100 gpd membrane in it and I don't feel that I need to replace our DI resin all that often. Granted, our tap water doesn't seem to be all that bad to begin with (compared to some I've seen), which probably contributes greatly to the life of our DI resin. It comes out of the tap around 250 uS/cm, out the RO in the 20 - 25 uS/cm range, and 0 uS/cm once it passes through the DI. I easily get 500+ gallons out of DI cartridge before I have to change out the resin in it.

How's that blue acro, schigara? The shot of it in your avatar makes it look like it's doing well in your tank.
 
The acro is doing very well and growing nicely.

fsn77 said:
I know a lot of people make a big deal out of that rejection rate difference, but our RO/DI has a 100 gpd membrane in it and I don't feel that I need to replace our DI resin all that often. Granted, our tap water doesn't seem to be all that bad to begin with (compared to some I've seen), which probably contributes greatly to the life of our DI resin. It comes out of the tap around 250 uS/cm, out the RO in the 20 - 25 uS/cm range, and 0 uS/cm once it passes through the DI. I easily get 500+ gallons out of DI cartridge before I have to change out the resin in it.

How's that blue acro, schigara? The shot of it in your avatar makes it look like it's doing well in your tank.
Click to expand...
 
So schigara your Dow Filmtec 75gpd has 98% correct?

Hopefully you can measure your in and out conductivity and we can compare that to fsn77's results for a rough experiment. I'd be interesting.

Maybe you can give a more accurate DI life and cartridge model fsn77. Then we can all know something new down the road. :)
 
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