Providing you do reasonably decent sized water changes, you should need to be worrying about Epsom salts.
You can raise MG by using either epsom salts, (Magnesium sulphate), or Magnesium Chloride.
The natural level of the ocean is 60-70% chloride and the rest Ca, Mg, Str etc, etc.
So this means that MG Chloride is the best to add. By ensuring decent size water changes, thye build up of extra chlorides is minimal.
I have heaps of SPS which have a high demand for MG and I only consume 3 cups of MG per week for 1400 litres. Its a reasonable amount, but by buying 25kg bags at $5.00 bucks a kilo its pretty darn cheap. Last me for months even with my size tank.