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What kind of RO membrane should we use in the Bay Area? (San Mateo specifically!)

Hey, I know there are two types (at least) of RO membrane. Everytime I need to replace one I forget which one we're supposed to get for our area. I believe we use Chloramine instead of Chlorine now.

Any help is useful!

Thanks!

Vince
 
Yes, chloramine is used in most CA water districts now (Bay Area has been on it for like 10 years). IIRC Chloramine is too small to be taken out by the membrane which is why you use a GAC filter prior for both chlorine and chloramine.

http://reefkeeping.com/issues/2003-11/rhf/feature/

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.
 
yeah, the thin film (organic??) membranes would get chewed up by the chloramine (metaphorically speaking)... your carbon prefilters make it a non issue though
 
Pentek makes a cartridge specifically for chloramines, look around, they are pretty easy to find.

If your TDS is low (I don't know what part of SM you live in), two carbon cartridges work just as well as long as you replace the initial one regularly. IME most of SM has really good water quality.
 
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