Extreme Gerbil Fighting - HELP!

Ok, i have three gerbils. last week i had to remove one of them from the
tank they were all in cause he was wreaking havoc in there on the smallest
one, so thats all taken care of.. he is alone in his tank and the two others
got the big tank. now tonight i see the smallest one, bloody as hell, going
in with teeth blazing. and i know he was the agressor (the small one) cause
he had all his injuries on his upper body, and the other one was hurt on the
tail and rear portion of his body, so now i took out the small one and put
him in a damn bird cage... im running out of tanks, and where i live, they
cost ALOT! i was sort of hoping to maybe put them back together again, but
that did not work. tried to put the little one with the first guy i took out
but they fought like crazy and i got my thumb bitten trying to separate
them.. so what do i do now? i have to have them separated forever now? im
sort of hesitant of buying them new mates too.. cause if that doesnt work
out, i gotta get even more tanks for the new ones.. i am in gerbil hell over
here.. some tips please. all the faq's say "separate them" when it comes to
fighting.. but it says nothing about for how long or what to do with them

Thanx for any answer