Danny,
You may have seen this article before, but here it is again:
http://www.advancedaquarist.com/issues/nov2002/chem.htm
And for good measure, an article on magnesium:
http://www.advancedaquarist.com/issues/oct2003/chem.htm
And for EXTRA good measure, the Reef Chemistry Calculator:
http://home.comcast.net/~jdieck1/chem_calc3.html
AND for EXTRA, EXTRA good measure, Aquarium System Volume Calculator:
http://home.comcast.net/~jdieck1/volcalc.html
You may be in for more water changes to drop your alk some more.