replenishing magnesium

[Beverly]

Quoted from halfway down the Magnesium link
http://www.advancedaquarist.com/issues/oct2003/chem.htm :

Epsom Salts (USP grade magnesium sulfate heptahydrate) is readily available in drug stores and very inexpensive. The problem is that if you were to raise magnesium by a large amount (or a small amount several times) the aquarium water will become relatively 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 experience frequent water changes. Bingman has addressed these enrichment issues and has suggested a recipe for home made supplements based on Epsom Salts and magnesium chloride. The problem is in getting the latter in adequate purity.