Dont even worry about the temporary side of it.
Most flake foods (as long as you dont buy the cheapest of the cheap) are suitable for the majority of species of tropical and cold water fish. You simply need to be sure that you are feeding enough and still have variety in the fishes diet to keep them healthy. i.e. also feed live or frozen food & veg.
Bear in mind however that a goldfish flake will have less "energy" in it per gramme as goldfish use less energy than tropical fish size for size. Coldwater fish in general live a slower life so dont use as much energy. So a goldfish may get fat if fed on tropical flakes alone and teh quantity isnt reduced.