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RO and Ion-exchangers

Hi all.
Another subscriber of the list, whom I have been mailing, suggested me to send this to the digest, so here comes:
+AD4APg- RO, in fact just beeing a very fine pored mechanical filter, takes out almost anything but water, even some bacterias, leaving about 99 +ACU- (or more, they claim) water with hardly any hardness or alkalinity.
+AD4APg- The most commonly known (it seems in the NG+ALQ-s, in USA, anyway) ion exhanger is +ACI-Water-Purifiers+ACI-. It is a +ACI-neutral ion exchanger+ACI- in connection with an active carbon filter. It exchanges Ca+-+- and Mg+-+- with Na+-, but does nothing to the anion, thus creating water with old fashioned washing soda and Na Sulfate. It is mostly regenerated with common table salt.
+AD4APg- Akvarists in Europe, using ion-exchangers, do one of two things:
+AD4APg- 1) use a weak acid KIE, that takes the kations of the weeks acids(H2CO3, primarely) A very common watertype
+AD4APg- like mine, TH+AH4-22, KH+AH4-16 ends up with a TH+AH4-6 and a KH close to zero. And that is really fine for most tropicals. I think it was Stanislav Frank who, in the 70+ALQ-ties made some investigation that showed TH is almost unimportant, but KH (and pH) was most important when it came to the hatching +ACU- of balck-water fish.
+AD4APg- 2) use a strong acid KIE ( takes almost all kations) AND ther after a strong or weak basic (anion E) takes almost all anions giving as a result +ACI-too good+ACI- water, like destilled(or even better, meaning less ions).
+AD4APg- I use method 2), but it is a pain .. .. ... to regenerate. Not the katioE (regenerates with HCL, that is easy and fast) but the anionE ( with NaOH, it takes like forever), so usually, if not trying to breed something special, I just use the kationE, getting water with about zero KH and a pH of 2-3, mix this with tap water to pH (after aeration)
+AD4APg- to about 6-6,5 and a kh+AH4-1. That suits me, but I might go for method 1) in the future.
+AD4APg- So, RO and the right IE takes KH, but +ACI-water softeners+ACI- makes unsuitable water if just a little XXCO3 in the tap water.
+AD4APg- Cheers,
+AD4APg- Ole