Get yaself a turkey frying rig !!!! it`s at least 85,000 btu
The slushy stuff is lead that`s cold , if this was happenin no worries of zinc contamination as zinc melts on the next notch higher heat .
To really clean the lead ya need it hot so contaminates can move to the top easier .
Be careful & not scoop off your alloys at lower temps , if ya had alot of fluffy stuff save it & flux it back in when ya get it hot enuff to melt good
I use pure paraffin to flux with it seems to make the alloys come off of the clips better & rust & dirt float better, it also seems to help mix the alloys better .