I would like to know how to:
     Convert the electrical conductance of my aquarium water measured
in milliSiemens (mS) to salinity and specific gravity.  The conversion
must be temperature compensated.  A formula would work best to do the
conversion.

If you can't find a formula, you could always make a few standard
saline solutions, measure the conductance at a few temperatures, and
use this data to make calibration curves.

You might find the PDF document below helpful to arrive at the correct formula:
http://www.cwr.uwa.edu.au/cwr/teaching/fm200_ivey/gi_equation.pdf

Regards
ldavinci

I agree.  If you can't find a formula, then set up standards, measure
them, construct STD curve and then examine the unknown.

There are ion -specific electrodes available.  Also, you migh contact
your neighborhood hospital and see if you could use the electrode(s)
found in their clinical chemistry lab.

Good Luck!