RO/DI questions

[spongebobby]

First off I have a 100gpd ro/di unit (horizontal di). I just recently changed the filters but not the membrane. Unit is almost 1.5 years old.

My water going in is 342 and after the membrane is 92. After DI is 0. My di resin seems to not be lasting that long and was wondering if it's time to replace the membrane and if so what membrane do you recommend?

:)

[sick1166]

probably best to change membrane. every 6 months change my filters and 1 time a year the membrane i probably use more water than you but i find membranes over a year really start to fall down

[Roland Jacques]

If you use good prefilters your membranes should last years for most reefers. But thier are lots of variables.

A good 98% rejection membrane should get you post RO water down to 7-8 TDS. Your DI will last 13 Xs longer than what your probably is now.

[AZDesertRat]

The most recommended membrane is the Dow Filmtec 75 GPD. At 98% rejection it is far superior to the 90% rejection rate 100 GPD version which isn't even a RO membrane at all but is a nano filter.
If you want the best DI life the 100% individually hand tested and guaranteed 98+% rejection rate Spectrapure Select series 90 GPD membrane is the way to go. The Select raised my DI refill life from 150 gallons per cartridge to 630 gallons per cartridge which more than offset the cost difference in just a matter of months. A good rule of thumb is for every 2% you increase the RO membranes efficiency you double the life of the DI resin so it makes a big difference.
Using high quality prefilters and carbon blocks also greatly extends the RO membrane life. Randy Holmes Farley recently reported almost 10 years out of a single RO membrane probably attributed to good filters.