I've read about 10 melanos per 1 gram of frog. Adults can weigh 7 grams, froglets around 1 gram. Very active and growing frogs need more. As long as you don't add so many that they stress your frogs out and there's not alot of strays the next day should be fine.
I realize you didn't ask about supplimenting, but wanted to mention you should be dusting your flies a few times a week with vitamins and Calcium D3 or an all in one like Repashy Calcium Plus.