View Full Version : How long does your DI resin last

06-09-2011, 08:42 AM
I am running two 150gpd membrane and i am using around 30 gallon of RO per week. My DI Resin only last me around 8 months when it start read 001

How long does your last?


phi delt reefer
06-09-2011, 12:26 PM
Coleus - i can't remember where i read this (might have been the spectrapure site) but maybe someone else can confirm this;

the 100+ gpd membranes have a lower rejection rate (~80-85%) while the 50-75gpd membranes average 95-98%. I would assume this means the DI resin in your system has to process more "after RO" TDS than the smaller systems so you will extinguish your DI resin faster than others.

06-09-2011, 12:35 PM
I think you are amongst the lucky few. Getting 8 months of use out of a DI cartridge sounds like a dream come true. By your math, you are getting near to 1000 gallons out of a single cartridge. That's pretty good.

I've only recently got my RO/DI system tuned in, so I can't say for sure how long the resin will last. I'd guess around 800+ gallons of water, but that's a pretty wild guess.

Its really more a question of how efficiently your RO membrane is opperating. If the TDS coming out of your membrane is 1ppm, your DI resin will last 5 times longer than if it is 5ppm.

The trick is to flush the membrane every time the system starts up and to allow the membrane to flush until it reaches an optimal TDS output. Any kind of start / start operation tends to be really bad for the membranes. Long periods without any use are also bad.

I run my top off RO/DI once a day to fill a resevoir. When the system starts up, it automatically flushes for 3 minutes via an electronic solenoid that bypasses the flow restrictor. An electronic float switch closes a second electronic solenoid as soon as the resevoir is full. There is a mechanical shutoff as a backup to the electronic system.

After a lot of trial and error, everything seems to be working perfectly. The RO membrane consistently produce water with 0-1 TDS. I expect my DI resin to last a long time.

06-09-2011, 02:07 PM
I have 2 10" DI canisters....I change 1 every month. Output after prefilters RO is usually 2-5ppm depending on the age of the membrane and prefilters.

06-09-2011, 03:18 PM
My 75gpd system has been processing water for just over 2 years & if my TDS meter is accurate, the DI is still good. I've kept a fairly detailed record of water produced, both RO only & RODI. Production to date is 335 US gal of RO & 1628 US gal of RODI, so total produced 1963 gal. My fish tank evaporates about a gallon a day & I do 25 gal water changes every 3 weeks. I make RO for coffee, drinking water etc, so reckon I use roughly 75 gals/month of RO & RODI. Tap water TDS is in the 210-220 range & I have the PRV (pressure reducing valve) in my home plumbing tweaked to provide just over 80 psi into the unit.

Couple of things I do in aid of DI longevity have already been mentioned by 'abcha0s'. I never run the system for short bursts, once I decide to produce water, I do a minimum of 5 gals. I flush manually for a minute or so before & after production. If I'm on the ball & think of it, I'll do a short manual flush during production as well. On start up, after flush, I close the valve to the DI cartridge & monitor the RO TDS output, sending the production water into a bucket until it gets down to 1 TDS. I then produce RO water only for coffee, drinking etc. Depending on how much RO I need, I may only run this way for 10 minutes or so, since after about 5 to 10 minutes, the TDS out of the RO is generally down to 0. This is when I open the valve to the DI cartridge & start DI production. Valving is all manual, nothing automated since I like to see what's going on.

So far the only filter I've changed is the 5 micron poly pre filter. I've also removed one of the carbon stages the unit came with & replaced that with a 1 micron poly pre filter. With no chloramines, the double carbon configuration is not necessary. So current config is 5 micron poly, 1 micron poly, 0.5 micron carbon block 'chlorine guzzler', 75 gpd RO membrane & DI.

phi delt reefer is correct in that the higher production membranes (150 gpd) have a lower rejection rate than the typical 75 or 50 gpd membrane. For the faster production rate of the 150, you are giving up some of the output quality, particularly if the incoming TDS is high.

06-09-2011, 04:20 PM
my dual RO membrane produce 5ppm at this time so i guess that explains why. Will try to flush more often. Thanks guy