I thought glycerin was pg. And that vg was the vegetable glycerin. So there is three? Where do you get them all? I tried Hobby Lobby, Walmart,(where I found USP Glycerin, bought) Can't find Vegetable glycerin anywhere. They look at me like I'm speaking a foreign language or something. Tried Health Food Store too. Nothing. I didn't want to have to pay shipping from anywhere. I went to Petco for Fluval or whatever it's called and they had nothing. Some of their filter/fluval looked like large pore sponge type. Then there was a no-name brand, that looked more like what fluval that should be used, but it was a huge box and they wanted 10 for it. No small packs. So me...being the tight wad I am,... didn't get it. Hobby Lobby had some LorAnns flavoring, but it sucked. Nothing I wanted. Grape, banana, cherry, etc. Had none of them. No glass dropper bottles. I tell you, this town had nothing to get. I did manage to find my hubby a wire stripper he wanted. I tell you, when ever I want something, never can get it. Always happens to me. If I don't want it, they will be giving it away at everywhere!! I am so aggravated now.