as much as the fish will eat in about 2-3 minutes. about 2 or 3 flakes per fish for tetras. 2-3 times per day. I'd stick with 2 so you don't end up over feeding. fish unlike humans (wel most humans anyway) will keep eating long after they have had their share. when I was a kid I fed a goldfish to death. I though beacues I dropped food in the water and he ate that he was hungry. not the case.
i agree with tanked but i feed once a day i would recomend feeding a neon scrunched up food as they have little mouths maybee two flakes at most see what they eat in a couple of minuets i give mine 5 mins but it should say on the side of the food packet what is suitable for that fish food.
i put in a small pinch of food, or a small squeeze of blood worms in jelly, every 2 days for my fish
some ppl might think thats cruel coz they'd be starving but at least im not over feeding them and i think its what it would be like in the wild.....the food wouldnt be easy to come by....but maybe thats just my opinion