This discussion is interesting, but I think that I should throw in an
example of how difficult the experiment for Calcium would be and that may
help a lot of people understand some of the problems on both sides.
An ordinary Hardness test kit measures both Ca2+, Mg2+, plus a range of
other ions depneding on their concentration and how tightly they bind to
EDTA. Calcium test kits rely on precipitating the Mg out of solution
first and then using the same chemistry to measure the concentration.
Neither test measures more accurately than 10ppm steps. A considerably
more accurate measurement would need to be performed eg the (probaly)
flame spectrophotometer that a friend of Bruce's has access to. This is
an expensive delicate machine to use and is expensive to run. It
typically can measure in the sub 1ppm range, the exact figure is
dependant on the machine and how the wind is blowing on that particular
day. Alternatively an even more accurate method may need to be used whic
relies on electronic monitoring of the current at particlur voltages and
this technique can measure in the ppb (ie parts per billion .001ppm).
Why all this talk of accuracy of Calcium levels? It is fairly simple, if
you are goijng to relate the depletion of calcium in the water to the
growth rate of fry it needs to be know accurately. You do not know where
the cutoff is for the fish being able to absorb calcium from the water. A
bone calcium test may be the best way in the end. Addmitadly this kills
the fish, but at least you know what is happening in the tank at that time.
Secondly there is the consideration of controls. Two tanks do not have
the same water chemistry even if they are filled with the same water to
start with. This poses a problem because it would be unknown if the
effect was water chemistry related or Calcium. secondly there is the
problem of sinks and sources, what if something was precipitating the
calcium from the water. I would presume that many of the organic acids in
solution would form insoluble precipitates with Ca. And there is also the
problem of external sources of calcium, eg food, water for water changes
etc.
I think that any sciewntist that tried to test this theory about Calcium
levels would rapidly find themselves in difficult experimental water with
a single rather shaky leg to stand on.
Sorry for this rather long post, I just thought that I should add a bit
in from a scientists perspective, even if I am running on the smell of
vegemite to gain a little "truth".
Peter Hughes