Scatter Gunner, If you are using a bottom pour pot, cover the melt with kittly litter, this will solve the need to flux. Marlevux is hydroscopic....it attracts water, so when you crank up your pot next time, be sure to lay all the spoons, dippers, etc that contacted the Marlelux on the pot so that the attracted moisture is driven off. DON'T stick thouse things unheatd into the melt....BIG NASTIES from that.
Melt down your alloy outside on a turkey fryer, flux all you want, used motor oil will do just fine, probably better than anything else you could use, lots of available carbon. After making ingots that will melt in your casting pot, just drop 'em in as required (I keep mine topped up) run your pot at teh lowest possible temp for good casting and it will minimize the oxidation that occurs, and that oxidation layer becomes the barrier that prevents further oxidation. Some use a laye of fine charcoal granules instead of the kitty litter, works well too.
A couple of exellent threads on this subject can be found doing a search for flux or fluxing at
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