New RO Membrane Rejection only 90%

[Tinkanator2000]

I just redid my RO unit, and went with a 75GPD DOW Filmtec membrane, and so far my DI has been getting eaten up pretty fast. Here is my set-up and associated readings:

Water feeds into a 5 micron sediment filter
1 micron sediment filter
5 micron carbon filter
.6 micron carbon filter
Hits a booster pump (boosts pressure to 50-55)
Hits the DOW Filmtec 75GPD membrane (has a 550 flow restrictor on the waste water output)
Then to the nuclear grade color changing DI resin from Bulk Reef

My readings are as follows:
Input 167 TDS and 5.25 pH (well water)
After membrane 17TDS
Water Temp after membrane is 60

My tap water uses a Sodium Hydroxide injection unit to raise the pH to 7, and I tried running the RO off that (normally I get the water prior to this injection), but it was even worse (about 260 TDS in and 40 TDS after the membrane)


What's the deal with the crummy 90% rejection rating? I made about 10 gallons of water, and ate up a good 8% of my DI resin.

Any help or tips on getting my rejection rating up to par would be greatly appreciated.

Thanks

 

[sirreal63]

I would replace the membrane that has a guaranteed rejection rate. Look at SpectraPure Select membranes, it takes the guesswork out of it.

 

[Tinkanator2000]

I had thought the Filmtec membranes were supposed to be the best?

 

[sirreal63]

The SpectraPure have a 98% and better and each is tested to ensure that rejection rate.

 

[uscgbeachbum]

This doesn't help your RO membrane, but I'd put your filters in descending order. Going from 5 microns -> 1 micron -> 5 microns -> 0.6 micron will severely clog your 1 micron filter.

 

[azjohnny]

have you measured the rejection water to good water to see what the ratio is? make sure it is 4/1. If you have too much back pressure in the rejection tube the membrane will become clogged

You may also have CO2 in the water ( which is common with well water) and this will cause big problems with the membrane. Here is a link that may be helpful

http://www.reefcentral.com/forums/showthread.php?t=1848403