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Upgrading RO/DI unit


cmanning

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We're fixing to upgrade our old RO unit w/ a RO/DI. How often does the DI cartridge has to be replaced? Also, does the carbon filter remove chloramine from tap water? One more question, what's the best place to order the unit from? Any information will be well appreciated.

Thanks,

-Cindy-

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I have an extra 100 gpd RO/DI system. Shoot me a PM if you are interested.

There are many types of DI resin with different life cycles. There is color changing DI resin that will literally change color when it needs to be changed. It seems that the life cycle is about 200-300 gallons. This resin also has always seemed to me to be lower quality. Then there are semi-conductor, medical, or nuclear grade resins. You determine when these have to be changed by using a TDS meter. When it starts reading more than 1 or 2 it is time to change. I have gotten 500+ gallons out of such resins. I would recommend using a refillable cartridge and using such resins.

Like resins not all carbon filters are created the same. Some of the cheaper ones will not catch all chloramine, but most will.

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I have had good luck with the refillable DI cartridges from http://www.buckeyefieldsupply.com. I like the prices and the DI resin I get from them. I have been using a .5 micron sediment filter (dont see them on the site anymore), a .6 micron Chlorine Guzzler carbon block filter, and the refillable nuclear grade resin. So far, so good. I have about 232ppm from the tap, about 5ppm after the RO membrane, and 0ppm after the DI. The better the water quality going into the DI the longer it will last. This is from a 50GPD unit.

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I have an extra 100 gpd RO/DI system. Shoot me a PM if you are interested.

There are many types of DI resin with different life cycles. There is color changing DI resin that will literally change color when it needs to be changed. It seems that the life cycle is about 200-300 gallons. This resin also has always seemed to me to be lower quality. Then there are semi-conductor, medical, or nuclear grade resins. You determine when these have to be changed by using a TDS meter. When it starts reading more than 1 or 2 it is time to change. I have gotten 500+ gallons out of such resins. I would recommend using a refillable cartridge and using such resins.

Like resins not all carbon filters are created the same. Some of the cheaper ones will not catch all chloramine, but most will.

Enigma13--Thanks for the offer...we are looking into a 150gpd/200gpd, we use quite a bit of RO and not just for water changes. I'm looking into the chloramine filters (kind of pricey) but I think it will be well worth it. We definitely getting an inline TDS meter, I'm curious and wouldn't be surprise about the readings. Thanks for the info.

jsr---Thanks for link.

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  • 2 weeks later...

Last week we order the SpectraPure MaxCap RO/DI unit. It arrive yesterday and was installed. I'm impressed on the purity of the water....I had to taste test it, since I have an RO unit under kitchen sink, I had to compare. I don't know how to describe it, but the water tastes great, weightless....if you could say that. I think our fish are getting spoiled.......now waiting on the skimmer.

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It is recommended that if you want to use one of these units for drinking water to put a T in the line between the RO stage and the DI stage. The DI stage strips out too much of the water. 100% pure water isn't necessarily good for you. It's not that RO/DI isn't good for you, RO is better.

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  • 2 months later...
We're fixing to upgrade our old RO unit w/ a RO/DI. How often does the DI cartridge has to be replaced? Also, does the carbon filter remove chloramine from tap water? One more question, what's the best place to order the unit from? Any information will be well appreciated.

Thanks,

-Cindy-

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!

RE Chloramines:

Carbon does not remove chloramines - but given adequate contact time, the carbon with split the chloramine into chloine and ammonia. The carbon will take care of the chlorine, and ammonia needs the be handled by later stages in the system.

Re where to order a system from... Well, we are a little biased on that topic!

Russ @ BFS

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