Google quote
“Hot Melt Adhesive (HMA) is called as Hot Glue, and is a form of thermoplastic adhesive. It is commonly sold as solid cylindrical sticks of various diameters. In the initial stage, glue remains tack when is hot, but later turns solid. It contains hot melt specific properties like Melt Viscosity, Melt Flow Index, Pot Life Stability, and few others. Hot glue gun consist of base material with various additives. Hot glue gun is non-toxic, but the fumes are quite dangerous “
Based on this it Doesn’t look like it should be a problem
Personally i would not test it on my tank i use the thick crazy glue (gel) with some Excelerator the bsi brand is reef safe might cost more but when things go wrong i won’t be thinking maybe its the hot glue i used