Be carefull with the epsom salts for Mg.If you use it alot you will raise your sulfate.This is from a RHF article found here:
http://reefkeeping.com/issues/2006-07/rhf/index.php
1. Epsom salts (USP grade magnesium sulfate heptahydrate) is readily available in drug stores and is fairly inexpensive. The problem is that if this were used to raise magnesium by a large amount (or a small amount several times) the aquarium water would become enriched in sulfate. This enrichment may not be a problem for some aquaria, especially those using salt mixes already deficient in sulfate, or those that employ frequent water changes. Nevertheless, Epsom salts alone is not an ideal magnesium supplement.
Check out chemMaster he has a Mg additive that will work for you at a good price.I think its Magflake,but you will have to ask him.