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Re: TDS readings

David did a pretty good job of defending the usefulness of a TDS meter
when rearing delicate softwater fish and indeed, for extrapolating
"hardness" when blending tap water and other water of known composition.

Since I suspect that its the osmotic pressure due to various salts in
the water that are most important, the TDS meter might be even more
useful than a "hardness" indication when dealing with water which has
mainly just the primary salts in it: (K, Na, Mg, Ca, NO3, Cl, CO3, SO4,
H & OH). Since TDS is really measuring conductivity, I'm not sure if its
that useful for organic solutes. For rearing delicate softwater fish, I
think we want to avoid organic solutes. For tropical-freshwater fish,
such as those from the Amazon, we might really want higher humic
concentrations which might act to inhibit bacteria. (but I'm straying
from David's original point) I suspect that many killifish benefit
indirectly from the humins derived from peat used for breeding. I wonder
if anybody has really tried to investigate the importance of humins for
breeding Tetras and Discus. Does anybody know?

My main point is that the word "hardness" is really a bad term because
it is so ambiguous. I'm going to get up on my soapbox for a moment;
please excuse me, but its a little hard to avoid getting lathered up
about this topic. I just find it so silly that, in the aquarium hobby we
continue to use this archaic and misleading terminology!

Are there any soapy apologists who would care to defend the use of the
"hardness" as a simple hobbyist term for describing the non-specific
concentration of dissolved stuff in water? Should we use hobbyist
terminology on this email list? Why use a five cent word where a half
dozen two-bit words will do? ;-)

Any pun~dits? George?

Specifically on this weighty matter, is there a better five cent word
than "hardness"? Is specific gravity better? I don't mean to be dense
about this... hee hee hee... ;-)

Steve Pushak                              Vancouver, BC, CANADA 

Visit "Steve's Aquatic Page"      http://home.infinet.net/teban/
 for LOTS of pics, tips and links for aquatic gardening!!!