Swordtail question

Because a swordtail had jumped into the tetra tank at the pet store they
gave it to me for free.  Well, I put the fish in yesterday to start the
cycle.  Everyone seems happy, the 4 tetras and the swordtail (10 gallon
tank).  The only thing is that the swordtail only seems happy until I put
food in the tank.  Then he just goes blank and doesn't even notice the food.
He has been trying to nip the tetras a bit, but they are too fast for him.
Anyway, how can I make sure that the swordtail eats?  I think it's picking
some up off the bottom, in fact I saw him doing that, but the tetras eat
everything so quickly that there really isn't much down there.  Is he
getting enough food?

Thanks in advance,

Ricky