Still think it's something to bring the levels up for my water changes I need to add nearly a cup of bulk Mg and I'm only changing out 20g at a time.

Well I picked up some Magnesium Sulphate Heptahydrate U.S.P from my Save on Foods. I needed grocery's so I thought I would check on the price and it is cheaper ($5 for 2kg). Yeah with magnesium chloride I am dosing the same ingredients as the Kent Marine product so I will get some of that aswell.

According to the Reef Chemistry Calculator I need about 500 grams... I don't have a scale... Approx how much will give me a 100 ppm increase?

yes thats the stuff. read this article, it will set you off on the right track.
http://www.reefkeeping.com/issues/2006-02/rhf/index.php
then use this calculator to figure out how much you need.
http://reef.diesyst.com/flashcalc/flashcalc.html
what do you have in your tank for corals, lighting, etc?
any questions just feel free to ask here.

All of my live stock is in my signiture. For lighting I am running 4 T5HO 24" Bulbs (1 Atinic, 1 Coral Growth(pink), 2 10 000K). I have 3 power heads (1 Koralia 2, 1 Koralia 750, 1 Koalia nano with the 2 and nano on all the time) Red Sea Prism skimmer and a fluval 405 canister (yes I clean weekly).

I have about 55lbs of live rock rangeing from 10 years old to new stuff and about 30lbs of live araganite sand.

I really should put my tank in the tank journal, but its not done yet :lol: (my wife saies it never will be... I tend to agree)