Solder's Flux Core is Bubbling and Throwing Small Solder Balls

[rg12]

Am using Kester 63/37 solder with a flux core, love them alot and using them for 3 years now.
I noticed that when I add alot a large drop of solder to a nickel tab or when adding solder to a copper busbar and creating a small "puddle" the flux (I think) bubbles and sometimes throws those super tiny balls of solder around which is stressing the shiz out of me.
Anything I can do to avoid it?

 

[marty]

safety glasses

 

[rg12]

safety glasses

It doesn't scare me for me, it scares me that I will end up with tiny metals balls running around a battery pack/bms...

 

[markz]

The solder is not properly adhering to the metals being joined. Apply a suitable flux/paste which cleans the surfaces for adhering of solder. Make sure you have the proper heat and that the heat is being applied properly to the joints and the solder.

 

[rg12]

The solder is not properly adhering to the metals being joined. Apply a suitable flux/paste which cleans the surfaces for adhering of solder. Make sure you have the proper heat and that the heat is being applied properly to the joints and the solder.

The main "blob" is spreading nicely on the surface it's being soldered on but when adding alot of solder there is more flux to play with and the flux is a bit "fizzy" under heat and from bubbling under the edges of the blob it sometimes throws out super tiny balls of solder that can roll around the soldered area.
I work on a black plexiglass tabletop so I can see the thinnest piece of fabric on it and I bet that if it wasn't for that shiny black table I would have never noticed these little solder balls.