Trace element question

[treygarz]

Im not sure if this is in the right place but here is my question: What classifies an element as being "trace"? Iodide, strontium, calc, and mag are all considered to be trace elements. However the range of concentrations vastly differes (i.e. iodide = ~.01-.02ppm whereas calc = ~450 ppm). Just trying to determine where the cut-off level is for "trace". Thanks for the input!

[Mr. Fosi]

Good question. Has Holmes-Farley ever written on this?

[lakshwadeep]

I think so. He does talk at least about strontium, iodine, calcium, and magnesium. Here's one example:

http://reefkeeping.com/issues/2007-04/rhf/index.php

 

Trace elements are those that are present at very low levels, i.e., less than 50 nM (nanomolar; about 1-10 parts per billion or so, depending on the size of the ion).