I see the links are working or at least some of them. I re-read Randy's article noted above and see that I was not 100% correct in my statement. Personally I have very high pH water say above 9, which IIRC Randy has stated at high pH the ro membrane does not remove ammonia well. But for lower pH level water (below 7.5), the ro membrane will remove a lot of ammonia. For clarification:
"Removing Chloramine From Water: Activated Carbon
Another method for removing chloramine from water is with activated carbon (as is contained in most RO/DI systems). In a two step process, the carbon catalytically breaks the chloramine down into ammonia, chloride, and nitrogen gas
C + NH2Cl + H2O � C-O + NH3 + Cl- + H+
C-O + 2NH2Cl � C + N2 + 2Cl- + 2H+ + H2O
where C stands for the activated carbon, and C-O stands for oxidized activated carbon. In this case, as was found for thiosulfate, the product includes ammonia, which is not bound significantly by activated carbon. Consequently, treatment of water with activated carbon will need to be followed up by some method of eliminating the ammonia.
In the case of a reverse osmosis/deionizing system (where carbon is usually part of the prefiltration prior to the RO membrane), the ammonia is partially removed by the reverse osmosis system. The extent of removal by the RO membrane depends on pH. At pH 7.5 or lower, reverse osmosis will remove ammonia from 1.4 ppm-Cl monochloramine to less than 0.1 ppm ammonia. The DI resin then removes any residual ammonia to levels unimportant to an aquarist.
Removing Chloramine With Activated Carbon: Does it Really Work?
There has been much debate over whether commercial RO/DI systems used by aquarists are actually removing chloramine in adequate quantity. The concern is not whether they can theoretically do so, but whether the actual units allow sufficient contact time between the water and the activated carbon for the units to do an adequate job.
I have been using a Spectrapure RO/DI system (CSP25DI) for years, and my water does contain chloramine, so naturally I was interested to know if it was up to the task. In discussing the issue with Charles Mitsis, President of Spectrapure, he said that my water was among the most difficult to successfully remove chloramine from because the pH was high, and he was not sure that the unit was adequate. The reasons for being concerned were that:
1. Monochloramine is the most difficult of the three chloramine species to remove because it is small (allowing it to pass through a reverse osmosis membrane).
2. Monochloramine is the most chemically stable of the chloramine species, so is the hardest to break down (as on activated carbon).
3. Monochloramine predominates over the other forms in tap water at pH above 7 (dichloramine predominates at pH 4-7).
4. The pores of the activated carbon may become plugged with sediment over time, reducing the effectiveness of the carbon at breaking apart chloramine.
5. At high pH, the pores of the RO membrane can swell, resulting in poorer rejection of impurities.
With this as the backdrop, I set about organizing a round of testing by aquarists to see if their commercially-available systems were adequately removing chloramine.
First, I selected a single, high quality test method for participants to use: the Hach CN-70 kit described above. I then asked aquarists to test several things:
1. The free and total chlorine in their tap water after letting it run for a while.
2. The free and total chlorine in their RO reject water.
3. The free and total chlorine in their finished RO/DI water.
4. The pH of the tap water.
In my case, for example, I had the following results:
Tap water:
pH ~9
Total Chlorine: 0.4-0.5 ppm one day, 0.08 ppm on a second day.
Free chlorine: <0.01 ppm (effectively all of the total chlorine was chloramine)
RO Reject water:
Total Chlorine: 0.02 ppm
Free chlorine: <0.01 ppm
Final RO/DI water:
Total Chlorine: <0.01 ppm
Consequently, within the capabilities of the Hach test kit (0.01 ppm), there is no chloramine getting through the system. A small amount does appear to get past the carbon to the RO waste water, but it does not get through the RO membrane and DI resin.
A similar set of data (more or less complete) was collected from about 20 aquarists in different parts of the country. These included systems that were stated to have a capacity of 25-100 gallons per day, the higher volume systems being especially interesting because the contact time with the carbon might be shorter. All but one had similar results to those reported here. The anomalous report produced the following results:"
