Do fish respond to GH or KH?

One for the chemists...

Karen writes:
> As far as I'm concerned, I have yet to see a method of reducing pH 
> in a planted tank other that within the carbonate buffering system 
> (i.e. using CO2) that is better for the plants  _or_ the animals 
> than just leaving the pH alone.  People who mess with the pH in 
> other ways are doing it for themselves, not for the tank 
> inhabitants.  
> ... almost any "community" 
> type fish can tolerate a pH of 8 if you don't intend to breed 
> them.

OK, I intend to breed some! :)
I'm trying to breed South American dwarf cichlids in my big planted tank.
Was just visiting cichlid guy extrordinaire Dave Soares, who said
basically that the species' ability to breed corresponds to the carbonate
hardness, because the harder it is, the tougher the eggs are (and less
easy for sperm to penetrate them).

Question: If I inject CO2 into hard water, will this effectively convert
all the carbonates into carbonic acid, thus being equivalent to naturally
soft water? i.e., is pH REALLY the indicator I should be keying off?

Side question: I just got a "Pinpoint" pH monitor as part of a fish &
plant trade-in at a store.  Are these things reputable?

   - Erik "Dr. Clueless"
   in Sunny Seattle

Erik D. Olson					         amazingly, at home
eriko at wrq_com