View Full Version : DI cartridge lifespan?
08/05/2008, 05:00 AM
I have your premium series 100gpd RO/DI unit, and it seems like I'm using up these cartridges really fast. One month ago I purchased a new sediment filter, carbon block, and DI cartridge. Two weeks ago I replaced the sediment filter again, and today the DI cartridge seems to be nearly depleted - based on the orange/brown ring being at the top now and my TDS climbing from 0 to 6. With all new cartridges my TDS reads 3-4 after the RO stage and 0 after the DI stage. The last DI cartridge lasted even less, but then I replaced the membrane also since my output decreased dramatically. I use Columbus City water.
I've owned the unit for 7 months now, and have replaced the cartridges 4 times and the RO membrane once. I produce an average of 500-600 gallons per month, sometimes more. Is it normal for it to wear out this quickly?
08/05/2008, 07:14 AM
Let's go through the filters one at a time.
Sediment filters will do just what you ask them - they will remove sediment. If you have a lot of sediment in your water, they will clog quickly. You can 1) replace them often, 2) place a sediment filter with a larger pore size (e.g., 5 mic) ahead of the 1 mic sediment filter, or switch over to a 5 mic sediment filter (which will allow the sediment smaller than 5 mic to pass.
A word of caution - be careful with how you match up the pore size on your sediment filter and the pore size of your carbon block. The carbon block should have a pore size about equal to or larger than the pore size of the sediment filter. So - using a 0.6 mic block with a 1 mic sed filter is fine. Using a 0.6 mic block with a 5 mic sed filter is not a good idea.
Are you changing the sediment filters based upon a drop in water pressure?
If the color change on your DI cartridge is at the TOP of the cartridge - that means that the DI cart was not packed with resin tightly enough, and the resin bed fluidized and the anion beads and cation beads have separated. Using a glass bowl right out of the dishwasher - dump the DI cart into the bowl, remix the DI beads, and reload the cartridge. This time settle the beads by tapping or bouncing the cartridge on a table top to get the resin to settle. add more resin and re-settle. Repeat this one more time and you should have a full, compacted resin bed that won't separate.
08/05/2008, 07:37 AM
Thanks. I changed the sediment filter basically because it took on a dark appearance, and I put the carbon matrix block in because the TDS leaving the membrane raised quite a bit. I don't really know what micron size I have, but I believe the sediment is a .5. I'll do as you suggest with the DI cartridge. Being somewhat new to the hobby, I really don't know what the normal lifespan of these components are (average gallons processed for example). I think my membrane was definitely bad, and it was only six months old, but the guys at Phishy tell me they typically last 1-1/2 - 2yrs?
08/05/2008, 07:57 AM
Yes - you should (as long as you don't leave your carbon in too long, or have odd water quality issues) get 2+ years out of the membrane.
Remember that the prefilters (sediment filter, carbon filter) don't remove tds. That is done by the RO membrane, and to a much lesser extent, by the DI resin.
The life span of the resin really depends upon the quantity and quality of the water you run through it. If the TDS of your RO water is around 5 ppm, you should get about 1000 gallons + or - out of a single cartridge.
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!
08/05/2008, 08:07 AM
Excellent information - thanks. I am running the MAtrix+1 I bought from your site right now. My TDS is the installed type, and it measures after the Ro and after the DI. I didn't understand all the functions as you describe above, but the TDS on the RO output went to 50+ and my output dropped (very suddenly) to 10-15gpd max. Before these clues occurred, I went through two DI cartridges in three weeks. The new membrane works great, so no problem there. My unit came with a pressure meter installed, it runs around 55 normally, but has dropped to 45 or so before I changed the pre-filters.
I just ordered a new Di cartridge from your site that I'l be able to refill.
Thanks for taking the time to help.
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