Cheap ways to boost Mg?

[mark]

Read that Epson salt by itself can cause a buildup of sulfate where as Magnesium chloride hexahydrate (available fr littlesilvermax) even mixed with Epson salt is a better choice.

[Snappy]

I mix my own and it's pretty cost effective.

[sharuq1]

How do you do it and what are you mixing and where can I get some Snappy? I pretty much want to just do this in a 5gallon pail, as that is my usual wc amount.