tail nipping, AGAIN

ok, so when my 4 fish (male swordtail, male guppy, long finned serpae
tetra, and "painted" tetra) were in my 10 gallon, someone was picking
on the swordtail and guppy and was biting their tails off. since i've
added all my fish in my 32 gallon i noticed my 2 new guppies suddenly
have a little slit in their tails. could it be the aggression between
the males since i have no female livebearers, or could it still be the
tetras? now do i have to worry about buying some females AND more
tetras so they focus even more on schooling or what?! gosh, pretty
soon i'm gonna need a 1,000 gallon tank just to make all my fish
happy!