Can tropical fish e.g. Neon tetras eat food made especially for gold fish?

The goldfish food is lower in protein than the diet for a tetra. Neons despite their small size are carnivores and goldfish are largely vegetarian. It would be almost like trying to feed your cat birdseed but not quite. There is some food value in it, but the pellets are probably too big. if you use it once in a while, it shouldn't hurt, but feeding goldfish food every day to a tetra would be a poor quality diet. Some fish like mbuna, cichlids from Africa that normally graze on algae can be fed goldfish food with no problems. If the pellets are too large for the fish, put them in an empty pepper mill and grind them small as you feed. Mark that pepper mill or keep it under the fish tank away from the dining table. Since you got it secondhand, check it for mold and decay. Pellets stuck together or discolored would be a bad sign. You could also smell it in case it has a sour or other off odor. I can't say fish food ever smells good, but it should have the usual fishy smell.

Yh I spose you could my goldfish sometimes eats mytropucal fish food when I'm out of goldy food and he's ok, so yh I guess so :).

its way better to use tropical flakes for both

yeah, food for fish is fish food.maybe itll make it bigger?