im affraid i have to agree. female gerbils can get very aggressive towards eachother, let alone the poor males.

if its any help, the tanks we use and the 20 gallon ones.

The general idea is 15 gallon for one gerbil and an extra 5 gallons for each additional gerbil.

Theres a great gebil forum for extra advice
gerbilforum.proboards21.com/index.cgi