How long have you had them in the tank? How long has the tank been set up? If it's a new tank and they are new to the tank make sure your tank is cycled! If its cycled and you added them after it was cycled I would do once every other day and give them as much as they can eat in 30 seconds between them. Then after a few weeks and everything is going well and they have settles in put it to once per day at the same amount. Then a few weeks later put it up to twice a day at the same amount.
This is how I did mine and my fish are all healthy and happy enough.
Glowlight tetra's 
