I have used hot glue to repair a crack on a hob filter it worked well it held up for months and the fish were fine i think its o.k. to use as a temperary fix from my expierence. I do know that there are different grades of glue for different projects i do not remember what type i used but it won't much of it just enough for a small crack for a couple of months then its new filter time maybe i got lucky.
I've used hot glue guns to make aquarium decorations for years. I've never seen any effect on the fish. It doesn't adhere well to polished surfaces or PVC use silicone to hold things better. I have used it to glue gravel to the base of plastic plants with good sucess, www.garf.org has done lots of testing, it uses super glue, its in the little tubes, very cheap, dont use crazy glue, ive used lots of tubes of super glue with no problems also, use a little sand paper to rough the pvc up before attempting to glue, for silcone i use ge clear door and window, any clear should work though just make sure it is not "mildew restant" its the mildew resistance chemicals that kill fish
Ya, a lfs near me was selling silicone like that with the mold inhibitor. Crazy. Well I will see how the glue from the glue gun works and I will rough it up on the pvc so the glue will bite, thanks for the info.