  Jump to Site Navigation  Issue: May 2007  Technical
Definitions  Author: Laura Muha  SF 0507 The Skeptical
Fishkeeper: May 2007   Technical Definitions  GH is an
abbreviation for Gesamthaerte. This is German for “total
hardness.” GH is the sum of divalent cations in solution. In
aquatic habitats, the vast majority of these ions are calcium
and magnesium.  KH is an abbreviation for Karbonathaerte, German
for “carbonate hardness.” This is a misnomer, since KH does not
measure cations; it therefore does not measure any type of
hardness. It measures anions that contribute to alkalinity. In
natural aquatic habitats the majority of these are carbonate and
bicarbonate.   Sidebar 2:  While many adult fish seem able to
adapt to water that is harder or softer than their optimal
range, they may not breed successfully in it. Water that’s too
hard may cause the outer membrane of a fish’s eggs to toughen,
hindering fertilization or preventing the eggs from hatching.
And if the water is too soft, so much of it may pass th