Re: Aquatic Plants Digest V1 #55

Kevin Conlin said....

>Having been hopelessly confused by the discussions on substrates,
>cation-exchange capability, and the like, I thought it might be
>interesting to try and eliminate the substrate altogether (hydroponic
>plants are normally grown with bare roots anyway).  This led to the
>following design:

Are you going to build it?

Paul Sears said....

>"alkalinity" is a term that is thrown around a lot without a
>clear definition being presented.  As far as I can make out, it 
>represents the amount of anions of weak acids present, i.e. those
>that can be protonated in the pH range that interests us, say 5 to 9.

Isn't alkalinity just acid buffering capacity? It's measured by
titrating to an endpoint. I believe this endpoint is pH 4.3 in the
case of the Tetra kit and is equivalent to methyl orange alkalinity.
So their kit measures carbonate and bicarbonate hardness, and
phosphates as well. The phosphates buffer in the pH range encountered
in our hobby. KH is a slight misnomer.