I think I may be doing something wrong. Have been buying smilin menthol cartos in 18. Ordered the same juice in 18 to re fill used cartos a few times. Is the juice stronger at 18 than the pre filled cartos? Also not nearly as good of flavor from the refilled carts as from the original pre filled carts, also much harsher flavor. I figured I must be doing something wrong in this process. Help anyone?