Does anyone know why glofish become agressive or possibly territorial?

I have a 5 gallon tank and I HAD a beta, goldfish, and two glofish and a regualr zebra danio. I am pretty sure it was the regular zebra danio that killed my goldfish, one glofish, and finally the beta. (all within a week!). I returned the three glofish to the store and replaced my fish with a new beta, bloodfin tetra and optimistically two glofish. all seemed well at first but the larger glofish began chasing the smaller glofish every time it swam past it. I took the territorial? glofish out of the tank for a day then put it back in this morning. When I get home I will see if it still chases the other glofish. I really want a varied tank of fish that are brightly colored which is why I chose the glofish to begin with. Any suggestions?