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Re: KATI (was APD V3 #1165
> I am getting the feeling that KATI is a great solution for people with > hard and alkaline water. KATI will replace the calcium and magnesium > ions with H+ and the H+ will neutralize the carbonate in the water to > reduce pH and produce CO2. And the KATI is rechargable with HCl, > which is commonly available. And there is no waste water.
> This sounds too good to be true. Is there a catch?
The first catch is that with hard water the ion exchange column will be
exhausted quite rapidly.
The second catch is that many waters do contain some CaSO4, (or other
sulfates) instead of only CaCO3. After the calcium is exchanged for H+,
one gets H2SO4 = sulfuric acid! Not good for fish nor plants!
That is why most commercial systems precede a cation/anion exchange
resins with a RO membrane that removes most impurities, leaving little
for the resin to do, that then "polishes" the water. The product can be
a _very_ pure water. But do you NEED such pure water? You must then add
back some salts for fish and plants to live. Many people just don't
purify it so well in the first place and mix with tap water for the
proper hardness or conductivity. One saves a lot of money that way!
A RO/DI combination has the advantages and disadvantages of both
methods. Unfortunately, the manufacturers seldom talk about the
disadvantages! RO/DI is used in analytical laboratories, where even
traces of impurities can not be tolerated and must be removed. For
aquarium use such water purity is NOT necessary.