Food Grade VS Agricultural Grade

[Myka]

I am ordering some fertilizers for my planted freshwater aquarium from www.aquariumfertilizer.com and I notice they have Calcium chloride for US$2.50/lb. With our dollar so strong, that is less than $3/lb, plus I can order another 2 lbs of ferts on my order and not have any increase in shipping, so why not? Good price. However it is agricultural grade, not food grade. I asked the vendor how pure it is, but she couldn't give me an actual number although she said "naturally occuring impurities". Well, Hydrochloric acid is naturally occuring too. I have always used food grade, so I am a bit concerned. Has anyone used agricultural grade? Does anyone know the actual numbers of purity? Should I be concerned at all?