How often to change Ro/di filters?

[CTurtleGirl]

I have a ro/di unit that I got a few months back. This is the first one I've owned. I am not sure when to change the filters on it or wich ones should be changed more than others. I have a TDS meter and the water still tests at 0 but I can see the filters discoloration (the housings are clear). If this helps I belive its a 5 or 6 stage filter. Thanks!

CTG

 

[Anonymous]

If its still reading 0 you should be fine. Usually the DI gets used up allot faster than the RO membrane.

 

[pcardone]

The manufacture of mine recommends replacing every 6 months. also run some chlorine through before installing new cartridges.

 

[KC36330]

the pre-filters before the RO membrane should be replaced when chlorine is detectable in it's output, chlorine will deteriorate the membrane shortening its life, the two carbon blocks are responsible for removing the chlorine. sense it's not practical for most people to test for chlorine, 6 months is a good benchmark, if you have a high demand from the filter then more often, a low demand, less often.

the DI should be changed when the output is 1/2 the TDS of the output from your RO.

kc

 

[Anonymous]

Well you're lucky to have clear housings, that's a bit of an expensive addition, think those suckers go for $20 a piece! However how often you need to change depends entirely on your water supply and how much water you put through them to "make" water, dirty water with lots of water changes you'll need to change the filters more frequently.

On the sediment filter (first one) it initially is white, if it starts looking like a medium-dark tea color I'd replace it.

Carbon filters (probably your next two filters), unfortunately the color test doesn't work well on them because the sediment usually pulls out most of the colorful gunk that would change them, most likely your first carbon is much darker than your second for this same fact that the first carbon will pick up any residual stuff that the sediment missed. Now the carbon's job is to remove VOCs and chlorine/chloramine, so again depends how dirty your water is... also depends how expensive of a filter you got, they range all the way from 5000gallons to 20000 gallon capacity, if you had the cheaper filters iniitially, changing them with the sediment filter is probably a good idea, if you have the longer lasting ones, which honestly I would only put one on the 2nd carbon filter spot, you probably can wait out another 2 sediment filter changes.

RO Membrane should be your 4th filter, unfortunately when to change it is really a tricky question, there' no real way to tell how bad it is unless you monitor the water before and after going in (which isn't a bad idea IMO) if it looks like it's pulling 90% of the stuff out (TDS) then it's fine, if it starts dropping, time to change, life spans I've heard on these are 2-5 years though sometimes longer. The one filter you need to worry the least of changing though now.

Finally is the DI resin, maybe 2 containers of it. Now color changing resin is nice... however I've noticed that a mixed bed color changing resin (at least the stuff I got) has a tendency to separate really making the color change useless unless you note which half is which. Now I have 3 chambers of resin, so the first chamber will change long before the 3rd so I have that visual que to let me know. But honestly use your TDS reading to let you know when it's time to change that. I wouldn't change it until I start reading over 10 TDS, reason why I don't say zero is because occasionally it goes out of whack, might be off a bit, but it gives you some leeway, however if you start to see it creep up each time you make water, you should change it.

Well hopefully this long winded explaination helped .

 

[Anonymous]

Yeah, the color changing resin does not reliably tell you when to change. TDS monitor should do a better job than what sfsu says it does, however.

 

[Anonymous]

A TFC mambrane should last from one year to 18 months depending on usage and that you change your prefilters when necessary. The foam block filter needs changing when it is either visibly clogged or the flow has slowed. The carbon block filter should be changed approx. every 3-6 months depending on usage and the amount of chlorine in your water. Those who use well water will usually need to change them less often. The main reason to change the prefilters is to get the max flow rate through the unit and too remove chlorine to protect the RO membrane. The TDS meter is a reliable way to tell if the mambrane and DI need changing.

 

[CTurtleGirl]

I'll probably change the first 3 that you guys are talking about. Just ordered the filters a couple days ago. I'm lucky that my tap water isn't that bad with a TDS reading of 26 but I can definitley see that the first filter is getting a pretty dark tea color look. Thanks for all the replies!

CTG

 

[Buckeye Field Supply]

From our FAQ list:

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