Some brand's aren't too good to do in huge amounts in a short period of time - large amounts meaning killing off half a tank or more to your face in one night, which a lot of people have been known to do quite often (that known personally and also have run into them on the boards every once in a while), just because of the other inactive and impure ingredients that are also contained within the whippets or within the tank itself. The dirtiest parts of full tanks are always near the bottom, since those impure/inactive chemicals are generally heavier than nitrous itself (all of them, actually, I don't believe there is any exception to the rule, but I'm not 100% on that). You can usually tell when a tank is getting REAL close to the empty mark when it starts tasting somewhat worse. If the tank is medical grade it wont have that negative aspect to it.
But anyway, if youre only doing low-to-moderate & average amounts of food grade during a days period, you don't need to worry too much. Only the worst brands would actually give negative effects for so little usage.
