View Full Version : Replacing filters

05/31/2009, 04:59 AM
I bought one of your premium RO/di units back in november. Don't i need to replace the carbon filter now? I am not sure totally how many gallons ran through(i would say not 20,000 gallons total though).

Do i need to replace the carbon block filter now?

Also, do i need to replace the sediment(first filter)? It isn't dirty looking and also the flow has not been reduced that i can tell. Would that filter only need to be replaced in these cases?

Thanks Russ for your help........

Buckeye Hydro
05/31/2009, 06:27 AM
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 then would otherwise have been the case. Sometimes the problem is poor quality resin – remember that all resins are not created equal!


05/31/2009, 07:05 AM
Well, a month ago i checked the water out of the RO after the resin and it was 0ppm. The last time i checked my water from my kitchen faucet, it was 250ppm. So, you advise to change the carbon block filter then? Does it exhaust pretty much after 6 to 8 months even if the 20,000 gallons total hasn't been ran through?

thanks, jack

Buckeye Hydro
05/31/2009, 08:06 AM
You want to check the tds in three locations:
feedwater: 250
RO: ??
DI: 0

After 6 months you should replace the sediment filter and carbon block. You are probably close to needing new DI resin.


05/31/2009, 11:51 AM
So, how long does the resin last normally if the RO membrane is fine? I bought the RO/DI unit back in november and again, it was your Premium 75gpd unit. Surely the filmtek RO membrane wouldn't be malfunctioning yet would it?

I will go ahead and replace the Carbon block filter and prefilter. How do you flush the carbon filter again(in case i lost my paperwork)?

Buckeye Hydro
05/31/2009, 06:50 PM
Resin life depends upon how clean the ROw ater is, and how much water you run through the DI resin.

4 to 8 months wouldn't be unusual.

Even if the membrane is fine, it may not be fully installed, or your membrane housing may be cracked - you won't know it unless you check the tds of your ro water.

Buckeye Hydro
05/31/2009, 06:52 PM
From our FAQ's:

Do I need to do anything special when I install new
cartridges in my RO or RO/DI system?

Well, yes and no. New sediment filters can simply be installed, and you're done. As for carbon blocks, RO membranes, and DI resin, that's another story...

Manufacturers recommend flushing new carbon block cartridges for at least 10 minutes before using the product water. Don't run the flush water through the rest of your system. Don’t run flush water through other stages in your system.

Manufacturers recommend flushing new RO membranes for up to 40 minutes to remove preservatives before using the product water. Don’t run flush water through other stages in your system.

Run 1.5 gallons of flush water through new DI resin before using the product water. Avoid contaminating (e.g., bacteria/mold/fungus) DI resin. Minimize storage time. Store DI resin in an airtight container to keep it moist until use. Store unused DI resin in an opaque container to avoid exposure to light. Clear shipping bags are inappropriate for long term storage. Treat your resin gently! If resin is exposed to freezing temperatures during shipping, allow it to warm at room temperature for 24 hours prior to use.

For those of you with chloramine issues, Catalytic GAC should be rinsed thoroughly, then wetted for 12 hours before use.

06/07/2009, 03:06 PM
Thanks for the info. I have installed and flushed the carbon cartridge. Now as for the issue on the Resin and RO membrane. How do i know if it isn't installed fully? I am very particular about doing things correctly(or you could say anal)and i am pretty sure i got it installed fully(of course that was 8 months ago). I also don't believe that there is any cracks in the housing(nothing has hit it). Again, if i test the water out of the RO membrane, what should it show on the TDS meter?

So, how long on average did you say that the Resin will last? What is the the longest it can last? thanks

Buckeye Hydro
06/07/2009, 05:14 PM
Check to see if your waste:permeate ratio is about 4:1. If you have the correct flow restrictor in place, and it the ratio is too low, many times the membrane isn't fully seated or the RO membrane housing is cracked.

Also, as you mention, check the rejection rate. If it is good, the membrane is fully seated and the housing isn't cracked.

The crack we are talking about here happens on the inside of the housing due to stress, rather than from being hit.

How long your resin lasts depends upon the tds of your ro water, and how much water you run through the resin.