Industrial = 92% pure, Food Grade = 95% pure, Medical = 99% pure.
The gas is all the same, the impurities come from the type of CO2 tank it comes in. Medical has a glass-lined CO2 tank, not sure about the others.
I use Food Grade from a home brew store, and I've been using it for a decade. Perfectly fine.
10 gallon acrylic fw planted. 6 HET rasboras, 2 otos, RCS, pond snails & MTS, ludwigia repens, Marimo & java moss, Eheim Classic 2211, Finnex Planted+ 17W LED, Hydor ETH 200W In-Line Heater.