Just re-built my 4-stage RO/DI for $53.35 (all filters & resin) + S&H

That's not a bad price.   I just got all new filters this week too.
This is a good reminder for all of the people out there with RO/DI units.   Don't forget to change your filter cartridges every 6-9 months and your membrane every year or 2.   If you don't, the performance of your filter will suffer greatly.
-JB

 

I"ll bet your sediment filter was the culprit. Just changing the filters on mine greatly improved output with the same year old membrane.

-JB

 

This might help (from our FAQ's):

A good rule of thumb is to replace your sediment filter and carbon block after six months. A more precise way to maximize the useable life of these two filters is to use a pressure gauge to identify when pressure reaching the membrane starts to decline. This is your indication one or both of the filters is beginning to clog.

Also be cognizant of the chlorine capacity of the carbon block. The Matrikx+1 (“Chlorine Guzzler”) for example will remove 99% of chlorine from 20,000 gallons of tap water presented at 1 gpm. Original equipment suppliers commonly provide carbon cartridges rated at 2,000 to 6,000 gallons.

Regarding your RO membrane and DI resin, use your TDS meter to measure, record, and track the TDS (expressed in parts per million) in three places:
1. Tap water
2. After the RO but before the DI
3. After the DI.

The TDS in your tap water will likely range from about 50 ppm to upwards of 1000 parts per million (ppm). Common readings are 100 to 400 ppm. So for sake of discussion, let's say your tap water reads 400 ppm. That means that for every million parts of water, you have 400 parts of dissolved solids. How do we go about getting that TDS reading down to somewhere near zero?

If you do some experimenting with your TDS meter, you'll note that your sediment filter and carbon block filter (collectively called “prefilters”) do very little to remove dissolved solids. So with your tap water at 400 ppm, you can measure the water at the “in” port on your RO housing and you'll see it is still approximately 400 ppm.

The RO membrane is really the workhorse of the system. It removes most of the TDS, some membranes to a greater extent than others. For instance, 100 gpd Filmtec membranes have a rejection rate of 90% (i.e., they reject 90% of the dissolved solids in feed water). So the purified water coming from your 100 gpd membrane would be about 40 ppm (a 90% reduction). Filmtec 75 gpd (and below) membranes produce less purified water (aka “permeate”), but have a higher rejection rate (96 to 98%). The life span of a RO membrane is dependant upon how much water you run through it, and how dirty the water is. Membranes can function well for a year, two years, or more. To test the membrane, measure the total dissolved solids (TDS) in the water coming in to the membrane, and in the purified water (permeate) produced by the membrane. Compare that to the membrane’s advertised rejection rate, and to the same reading you recorded when the membrane was new. Membranes also commonly produce less water as their function declines.

After the RO membrane, water will flow to your DI housing. DI resin in good condition will reduce the 40 ppm water down to 0 or 1 ppm. When the DI output starts creeping up from 0 or 1 ppm to 3 ppm, 5 ppm, and higher, you know that your resin needs to be replaced. Sometimes people complain that their DI resin didn't last very long. Often the culprit is a malfunctioning RO membrane sending the DI resin “dirty” water. This will exhaust the resin quicker than would otherwise have been the case. Sometimes the problem is poor quality resin – remember that all resins are not created equal!

Russ @
Buckeye Field Supply

 

Thanks for the input Russ!! This info should help members to tune their RO systems.

 

Great info, Russ! Thanks and when I need something for my RO/DI, you're the man!!

 

also, if you have a water softener, run it before the RODI, as the Sodium ions from the sodium carbonate are much eaiser for the RODI unit to strip from the water.

You can get water so clean and pure it is a sponge for anything that touches it and quite unstable (it will change PH VERY rapidly by just blowing on it)

 

I know this is an ancient thread but...

Just happenned to look at this thread and saw Eric's picture of his (then) new filters. Be careful to check the specifications on your filters when you buy. That sediment filter is a 25 micron filter! Unless you are using that in a whole house filter, or follow it up with better sediment filters, 25 micron is not what you want.

Russ

 

What RO/DI units do you guys use? I am looking at picking one up in the next couple of weeks here, so far I've been using treated tap water which I now understand is a no-no.

 

I got mine from The Filter Guys. Great support, and great quality. I think they're in Minneapolis, so shipping is really fast.

 

I'm a big fan of my RO/DI unit from Air, Water, and Ice:
http://www.airwaterice.com/product/1EXTREMETYPHOONIII/EXTREME-TYPHOON-III-150-GPD-RODI-with-Gauge-TDS-Alarm-Dual-TDS-Meter.html

This thread reminded me that it's probably about time to replace my filters /DesktopModules/ActiveForums/themes/_default//emoticons/sad.gif
$47 for the prefilters and DI resin (I replace these annually)
$50 for the 150 gpd RO membrane (every two years)

 

Think:
1 micron depth filter
cat GAC
0.5 mic carbon block