Personally, I've always used 1/4t a gallon, but it seems very common to use 1t/g. I just always feel better using less of anything if I can. If I don't see the level of results I feel I should, then I add more, up to 1t/g. Hope this helps.I have a Mg defiency and using Epsom Salts. How much Epsom Salt for a quart of water to spray? How much Epsom for a 27 gallon hydro reservoir?