when do i replace cartridges in RO/DI?

[scarf_ace1981]

guys i've had a 6 stage RO/DI for maybe 3 months. i noticed that the bucket i use to make water changes is filling up a lot quicker. last night i used my TDS meter and it said 001-003(RO/DI). what does that mean? by the way my tap water read 032.

reason i ask is cuz i'm getting a little just a little cyano. nothing problematic but i'd like to know if it's time to change the cartridges.

thanks
jon

 

[jawwad2004]

Are you using the aquasafe unit?

 

[DEEPWATER]

you should have a tds meter to check with
the other filters i usually change every 6 to 9 months .
Membrain i change once every year .no matter what the meter says

 

[aaron23]

one way to see is the DI resin may change color mine goes from green to brown.

 

[scarf_ace1981]

jawwad i'm using the aquasafe.

like i said b4 the TDS meter read 001 for my RO/DI(it hit 003 but then went to 001).

i'll look @ the resin beads.

 

[joseney21]

how long have you had the unit??

 

[Buckeye Field Supply]

Sorry if anyone has seen this post before, but the question keeps coming up:

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 filers is beginning to clog.

Also be cognizant of the chlorine capacity of the carbon block. The Matrikx+1 (?Chlorine Guzzler?) for example will remove >90% 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 ppm. Common readings are 100 to 400. So for sake of discussion, let's say your tap water reads 400. 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 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 permeate, but have a higher rejection rate (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. How do you measure TDS? With a meter like this: http://www.buckeyefieldsupply.com/showproducts.asp?Category=42&Sub=1
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. Usually 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.

 

[michaelp]

From: Michael H. Pryor
Sent: Tuesday, June 13, 2006 1:29 PM
To: techsupport - aquasafecanada.com
Subject: DI/RO/Other


>> Can you give me the replacement gallons (i.e. after how many gallons of
water, do I need to replace these things)

>> DI media?

No...this depends on tds and rejection rate of the RO...most homes seem
to get around 2,000 or so

>> RO membrane?

Years...at 3500 gallons per year, and proper flushing 15,000 to 30,000

>> 3 other filters on the unit?

Average home 6 months

Best Ed