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:
Tap Water:
pH 8.2
Total Chlorine: >3.5 ppm
Free Chlorine: >3.5 ppm
Filtered Tap Water: (single cartridge under sink, cold water side)
Total Chlorine: 0.7 ppm
Free Chlorine: 0.38 ppm
RO water: (11 month old cartridges)
Total Chlorine: 0.16 ppm
Free Chlorine: 0.06 ppm
RO/DI water: (11 month old cartridges)
Total Chlorine: 0.04 ppm
Free Chlorine: 0.02 ppm
RO/DI water: (Fresh cartridges)
Total Chlorine: <0.01 ppm
Free Chlorine: <0.01 ppm
In short, his tap water chloramine (and chlorine) levels were quite high. His old carbon and sediment cartridges were not quite up to the task, but when replaced, were adequate to remove all of the chloramine. Note that the 11 month old cartridges were still producing 0-1 ppm TDS RO/DI water.
Lessons Learned and Suggestions:
1. Most RO/DI systems seem capable of removing chloramine adequately for aquarists.
2. The carbon cartridge may become less useful over time, and it is possible that the chloramine removal effectiveness of a system may be lost before the DI appears to need changing.
3. Cheap sediment cartridges may expose the carbon cartridge to unnecessary fouling, which may permit chloramine to pass through the system. Cartridges should be replaced as soon as the pressure drops significantly, even if RO/DI water is still being produced at a reasonable rate or purity as measured by total dissolved solids.
4. Testing for chlorine and chloramine is easy, so any concern is easily reconciled.
5. One Hach kit provides several dozen test results. Our local Boston Club bought some kits and had a "water testing day." The kits can also become part of the "library" of a local club for aquarists to use once in a while to see if their systems are functioning. That way, the cost to each aquarist is minimal.
Conclusions
Chloramine in tap water should be a significant concern to aquarists. Its peculiar properties make it well suited to disinfection of water supplies, but also make it a potential toxin in aquaria. In order to render the water safe for use, aquarists need to use one of two systems for purification: an inorganic reducing agent combined with an additive that binds ammonia (or a single product that does both), or an RO/DI system. Chloramine is toxic enough that it would seem prudent for aquarists to spend the time and money necessary to ensure that they do not unduly stress their organisms. This activity includes setting up appropriate purification systems, and may also include testing the water to ensure that those systems are functioning properly.
Happy Reefing!
