After doing a fair amount of reading I'm gonna pass on this product. Read a few articles stating that MgO can be pretty toxic plus I don't know what else it may have in it.
The good news is I located muriate of potash. No pottery stores in the area so I paid up and purchased a box of API first layer laterite which should provide the iron. Also started the first soaking and drying cycle on two big bags of Earthgro topsoil. I had a bunch of crushed coral left over that I pulled from my reef so I am soaking that in ROdi water and changing it daily while the soil is mineralizing. That ought to draw all of the salt out, and I'll just use Epsom salt for the Mg element.
People say MTS works so well but is too much work. Luckily for me I don't really find it that bothersome so hopefully this batch turns out better than the last. It's been 2 years since I paid any attention at all to my planted tank so I am long due for an overhaul! Thanks for the replies.
Also, anyone have any ideas or articles they can point me to that outline specific amounts of these things needed for a 75 gallon?