Hey Habu,
I just posted a comment about your question on Lubrisizers, and now I see this question, so I will give this a try also.
My comments will be based on the assumption that you are starting with a basic alloy of lead, tin, and antimony which you probably are if you are starting with wheel weights for a base. If, on the other hand, you got some exotic concoction that contains other metals, my comments will not be appropriate. It is always good to start with a basic lead, tin, antimony (LTA) alloy.
When you melt your LTA alloy, the mixture will slowly get hotter. If nothing is done, eventually the tin and antimony will start to rise to the surface and will appear as a discoloration on the surface. Dirt and other impurities will float on the top of the alloy and should not be confused with the tin and antimony.
When you fluxed the mixture with a chunk of candle wax, you should have used a casting lade to stir the mixture (dirt and all) very thoroughly for a minute or so. At that point, the wax should have been consumed in the process, and all the discolored surface material should have disappeared back into the mixture - leaving a surface that is bright and shiny like a mirror. The dirt and residue that remains on the shiney surface should then be removed with the casting ladle, and then the casting process can begin.
If you use the ladle to stir the mixture a little each time you fill the mould, you can cast quite a few bullets before the tin and antimony start to rise to the surface again. Once you see the surface of the mixture is no longer bright and shiney, it is time to flux the mixture again. When using wax for fluxing, allowing it to ignite makes for less smoke in the process. However, you must obviously be aware of fire hazards in the area.
No, you do not want to remove the material on the surface of your alloy that is making it discolored. That is the tin and antimony you want to make your alloy hard. You want to flux, mix it up so the surface is bright, and then remove the remaining dirt and dross. Never remove dross and dirt unless the surface of the melt is bright and shiney.
I am not sure what you mean by "Is it common to have to flux your small casting pot when casting bullets?" However, as mentioned above, you have to continuously flux your mixture as you cast bullets and refill your pot.
Best wishes,
Dave Wile
