When to change ro/di filters

[bmrescort]

Do most people here change filters on a pre-set number of months or is there a way you can tell when they are exhausted of use. I have had mine online for about a year and have the original spectr-pure filters in there.

Just curious of what others use as a basis for changing filters.

 

[a2fire2i]

I change mine every 6 months or so. If you have a pressure gauge on there, you should start to see it drop and that is a good sign that they need to be changed.

 

[Nanook]

I use a pressure gauge on the sediment pre-filter, so when there is a change in pressure of 10-15% or it becomes dark yellow I change it. I think 6 months is pretty average for sediment filters and carbon filters depending on how much water you make. I use color-changing DI resin and have a TDS meter and Spectrapure monitor on the output water. The main thing is to make sure you change every six months at least and keep the TDS at zero, zilch, nada.

 

[Nanook]

RO membranes can last 2-3 years no problem.

 

[bmrescort]

Thanks for the input. My output reading for tds is not exactly zero so I think that it is time to change out the filters. I know that alot of people have different preference on where they buy filters but Nanook do you think I should buy them from spectrapure since that is the unit that I have?
My color changing resin is about 1 inch from the bottom of the holder so I know that it is not exactly 100% used up but I think now is the time to change it.
Let me know what you think and thanks for the remarks guys. All in all the tank is doing great after 1 1/2 years I really need to figure out my camera a bit more so I can post some pics.

 

[Shooter7]

Wouldn't the frequency of changing really depend on the amount of usage? I would think that someone with a 200g system would use considerably more water in topoff and water changes than someone running a 20g system, and therefore would "use up" their filters more quickly. The place I got mine had suggested replacement at about a year, given my usage, however, I'm nearing a year and don't see any real color changes in them so not sure I can count on that as a reflection of their lifespan. I don't have a pressure gauge - are they really that vital for the use of the unit? I haven't ever really seemed to need one.

 

[Nanook]

I've used Spectrapure for years and have really liked their product but now that I use so much RODI, I have found their pricing to be prohibitive. I talked with a guy at The Filter Guys here on RC by phone and he is very personable and helpful...their pricing on filters and resin is tough to beat as well. FWIW, I have all Spectrapure housings, but have went to a different company to save money and still get great water quality.

 

[Buckeye Hydro]

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 â€"œ remember that all resins are not created equal!

Russ @ BFS