🚀 go-pugleaf

fernando@aplcomm.jhuapl.edu (Fernando Pineda) writes:

>I was looking at Martin Moe's Marine Reference book and I'm puzzled by
>his dKH conversion (cf. p. 36) . Sea water should have ~400 ppm Ca+2 ions or 
>equivalently, ~1000 ppm CaCO3. Now if I take his conversion to dKH I either 
>divide ppm CaCO2 by 17.9 or multiply by 0.05 (I'll forgive his approximation 
>0.05 ~1/17.9).

[calculations deleted]

You're confused on the various hardnesses.  You're trying to equate
calcium hardness with carbonate hardness.  Both are measured as CaCO3
by the test kits available.  The 17.9 conversion is for carbonate
hardness.  To confuse things even more, total hardness is also
expressed as equivalent amounts of CaCO3.

Generally speaking, when "hardness" is mentioned with respect to
seawater, they're refering to carbonate hardness.  That hardness is
some 7 german degrees or 3.5 meq/l in "standard" seawater.

Calcium hardness is measured to insure sufficient calcium for inverts
to use.  As you cited, a value of 1000 mg/l CaCO3 = 400 mg/l Ca ion
which is a good value to keep.  I keep my tank between 400-500 mg/l.
The Halimeda seems to do better when things are closer to 500 but I
also find more limestone deposits at those levels as well.

It took me a long time to get the hardnesses straight in my mind, and
I'm still not sure I have a complete understanding of them.
-- 
Keith Rogers
krogers@javelin.sim.es.com