View Full Version : On average, how long do your RO/DI filters last?

01/26/2009, 10:15 AM
I have a good 5 stage RO/DI and I’d like to know how often I should change my filters. I heard the R0 membrane last for 5 years or so, but I’m not sure about the others. I normally just change them all at once when I my TDS gets above 4. Is there one that should get changed faster than another? I feel I might be wasting money, the way I’m doing it now. Here’s what I run:

Stage One - NSF rated 5 micron poly sediment filter

Stage Two - 5 Micron Matrikx NSF rated CTO/2 Workhorse carbon block

Stage Three - 0.6 Micron Matrikx NSF rated chlorine guzzler carbon block

Stage Five - refillable cartridge with color-changing DI resin

01/26/2009, 10:19 AM
here's what i understand a good schedule to be:
prefilters and carbon block: 6months
di resin: will vary, when tds starts to creep up past 1, change
ro membrane: should last years, check efficiency by measuring tds before (tap) and after. when the rejection rate starts to drop, it's probably time.

01/26/2009, 10:21 AM
+1 for the above. six months for prefilter, carbon. DI resin usually doesnt last much longer than six months either. ro membrane should last about 4 years.

01/26/2009, 10:31 AM
I have never really checked my filters but am still getting ZERO TDS. I have been running them for almost 2 years with no backflush. I have filled a 75g and a 200g and top off about 4g per day.

I did need to replace my DI resin about 6 months ago I was reading 3TDS changed the resin and still at ZERO.

I calibrate my TDS meter every other month.

01/26/2009, 10:39 AM
di resin alone will make 0 tds water. how long that lasts depends on the tds of the incoming water. the prefilters are there to aid in the efficiency of the ro membrane by filtering out larger particles, and the ro membrane is there to filter out smaller particles. once that's done the di resin doesn't have to work as hard and therefore lasts longer. in short, you'll still get 0 tds with prefilters that need to be changed if you've recently changed the di resin, but you're shortening the life of that resin by not properly caring for the rest of your unit.

01/26/2009, 11:08 AM
I just changed everything at the six month mark. I have the color changing DI resin and it was less than 1/2 changed. The prefilter was very dirty. My tap water tds are 100 which isn't too bad.

I was making water for a 74 gal and 29 gal for water changes and top off. I backflush my unit often.

My tds were reading 1 or 0. I probably could have gone longer but when I saw how dirty the prefilter was I will replace faster in the future. I also have a 280 gal tank now so I will be making much more water.

I estimate that I will need to replace the prefilter and carbon every three months and the di resin at 5 months. I don't feel this is a huge expense compared to what everything else in the hobby costs. I pay more for salt than I do for cartridges.

01/26/2009, 01:51 PM
On average, what should the TDS be leaving the membrane, before it goes through the DI resin?

Secondly, how do i backflush the membrane? Mine has the valve on it, but I never really knew how to do it, or how often, so I've never messed with it.

01/26/2009, 01:58 PM
i changed my prefilters at 6 months. then changed my DI resin 2 times in a year, once at 8 months and another at just 4 months. not sure what happened there, but it was color changing and was mostly changed. I run redundant Mixed bed filters, so once the first one is changed, i rotate #2 into #1, and refill #2... that way i know when #2 starts to change, i know #1 is exhausted.