Re: Do fish respond to GH or KH

> 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).

I take it that by 'carbonate hardness' you mean KH? ... which as we all 
know is not 'hardness' at all but alkalinity (ie. a measure of the amount 
of inorganic carbon in the water ... mostly). GH, on the other hand, is 
actually a measure of 'hardness' (ie the total amount of alkali earth 
metals in solution ... Ca, Mg etc.).

> 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?

This is a very intersting question. Injecting CO2 does NOT alter the 
alkalinity (KH, carbonate hardness) of the water. It decreases the pH by 
altering the ratio of H+ to OH- in the water. A charged acid such as HCL 
or H2SO4, OTOH, will lower the alkalinity as well as the pH. Changing the 
alkalinity, however, will in no way 'soften' the water as this is 
determined by divalent cations (alkali earth metals) such as Ca and Mg.
So ... there are three factors at work here ... pH, alkalinity and 
hardness. They are all independent but related factors and you must know which
one is critical before you can determine which one to control ... my 
instinct is to suggest that they are all important in breeding success. 
In other words, you should probably lower the alkalinity, pH and hardness.

dr. dave