I use 1 teaspoon of white sugar per 12 oz bottle. And I put it directly into the bottle first, then bottle the cider on top of it. Sometimes when you mix sugar into the bottling bucket, it doesn't dissolve fully or evenly, and some bottles get more sugar, and some get less. We've had much more...
Hey Semicole,
Arlington brewer here- so I'm not sure about the Plano area, but there's a place called Kool Keg (http://www.kool-keg.net/) that we get our refills from. An option if you're in the area for something else!