Definition of alkalinity

[<Stephen.Weir@csiro.au>]

Dear all,

This is probably not of specific interest to apisto fanciers, but is a more general aquaria topic.  I do however know there are a few chemistry competent keepers on these lists.

As a bit of background, I'm reviewing an information sheet on water chemistry for ponds and the author wishes to use the term alkalinity.  To me as a chemist alkalinity is the opposite of acidity, and so implies an excess of hydroxide ions in solution.  The OED defines it as "the quality of being alkaline; alkaline character or property".

However I know that in dumbing things down many aquarium book authors have twisted the meaning to indirectly represent carbonate hardness, since the overwhelming majority of alkalinity in natural waters is due to carbonate/bicarbonate.  They then twist it a bit more, since carbonate/bicarbonate is also the buffering system in natural water, and alkalinity then becomes equivalent to buffering capacity.  The definition of alkalinity most often suggested by these authors is "the resistance to pH change upon addition of an acid", which is a long way from what I take alkalinity to mean.  They even quote alkalinity in terms of degrees or ppm, which I know refers to CaCO3, and is alkaline, but it still irks me.

What I'd like is for anyone that can find a definition of "alkalinity" related to aquaria to please let me know of it.  If the author of the information sheet I'm reviewing insists on using the term I at least want to have an accepted definition I can quote and reference.  Or if anybody can propose a different set of definitions that are familiar yet accurate I'm all eyes :)  

FWIW, I checked the krib but the main article on carbonate hardness (by Larry Frank) actually has several errors in it.

Thanks in advance to everyone,

Steve    

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