Aquarium safe Garbage can ?

[DEAD_BY_DAWN]

I was helping a friend tear down his tank for a over haul
So as pernormal (not with this can)Fish were housed for about
Two hours heater pump etc.
Mid way through I went to check on them to find them all gasping
At the surface and turning pale .
Long story short a few died turns out this can contains
antimicrobials possible cause of fish death ?
Not really sure .
Can was cleaned before use.