Thank you for finding this out and taking the time to share it. I had been trying to google this exact information last week and put down a SMaSH with their ale grain (1.044og) and por (24ibus) yesterday as I assumed the recipe would of changed now they malt in house. I even adjusted my water...
It does not need to be medical grade. The ones from Reece/bunnings etc are food not medical grade. Medical grade has no moisture making it safe for breathing in. The filter is for the fish pond set up and not required for o2.