Ro/DI Replacement?

[mspad]

How often should RO membranes be replaced?

How often should DI filters be replaced?

How often should the carbon filters be replaced?

I am currently producing about 150 gallons of RO/DI water every month. My concern is that I am not changing them enough. I change all of the filters about every 6 months.

Any thoughts?

[AZDesertRat]

Prefilters and carbons should be changed every 6 months and the housings should be disinfected at the same time.
Membranes usually last 3+ years IF you keep up with the 6 month replacements and disinfection and use high quality filters, not e bay cheapies. The only way to tell the condition is with a TDS meter, when RO only TDS rises its time to replace it.
DI resin is entirely dependent on how much water you make and how well the RO membrane in working. Again a TDS meter is the only way to tell the DI condition. You should not have a RO/DI unit without having a handheld TDS meter.

[shikhyung]

I have a TDS meter. I have not checked the reading yet, but should I go ahead and change the resin since the color has changed anyway. Last collect ( week ago, reading still 000).
Also, I heard the term making sure the resin is packed... how do I know it is packed?

Shin

[AZDesertRat]

Color changing resin is a poor indicator or resin condition. Always use a TDS meter!
To ensure the resin is packed tightly, when filling the cartridge, fil it to the top, tap it soundly on the counter or table top a few time, add more resin and do it again a few times. You want the sponge pad on the end to fit snugly. This will eliminate any voids which lead to short circuiting or channeling. Resin actually shrinks a little over time so if it is crammed full you will not have any problems in the future.

[BuckeyeFS]

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 its 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 then would otherwise have been the case. Sometimes the problem is poor quality resin – remember that all resins are not created equal!

Russ

[mspad]

I wanted to thank everyone for there help. I have ordered a TDS meter and can't wait to see the findings. I will post them as soon as I can.

Thanks again

[Myka]

Thanks for that post Russ! Gave me all sorts of new info on my new RO/DI that I don't know much about.

[BuckeyeFS]

You're welcome.