@ Kestral: The only real recommendation on tank size for a single betta is nothing smaller then a 1gal.. it's that a lot of people think they have to be in 2.5+, which is untrue.
No matter the size of the tank and the amount of girls, there is always a high risk of fighting. It's a risky thing and it doesn't depend just on size of anything. The reason for the recommendation of 5+ is because when they DO fight and chase, there will be more girls all around to take it instead of just one or two who are continuously chased to death. Think of young girls of say, 12 years old... we're best friends today.. oh wait, she has something I want.. I don't like you! Oh hey you want to share? Okay we are best friends again.. back and forth. No matter if they lived happily for 2 years like that, all it takes is just an instant and one is majorly hurt or dead and you will never know the reason. And you'll be sitting there stumped going "Well, they were ok together yesterday".
Sadly, that's the sorority life.. you just never know and it's always a risk. How about dividing the 5 into 3 slots? A little over a gallon each, which is enough space to live comfortably, and yet be safe.
Don't want to sound rude.. but you read/hear a lot of "well they were fine this morning, don't know what happened" stories and having fewer with a smaller tank makes trouble happening greater. =(
Last edited by Myates; 09-19-2011 at 08:21 AM.