Betta tank size for females?

Two females IS a problem in a 2.5 gallon. It isn't space, per se, rather it's territory: 2 cannot be kept together as 1 will bully the other over it's perceived territory, which is everything that is in their range of site. These problems can take a week or 2 to sometimes appear, so I'm implore you to either get to separate tanks or do a larger tank upgrade & put them in it (after cycling it, of course).

There's a myth that females are the nicer, gentler sex of betta & while that can be the case, it's no guarantee. I can tell you from unfortunate personal experience that you can do all the right things & do all the proper planning, have all the right equipment & do it all to the letter & sometimes those female bettas have entirely different ideas. The way females act alone is often strikingly different than how they act when in contact & competition with other females. Think of it like high school-there's the girl that's always nice to you in class but as soon as she's with her friends she acts entirely differently-it's the same with female bettas. Females flare, fight, chase & bite other females & can be just as territorial & aggressive as males. Females consider anything in their line of vision to be "theirs" and will fight & even kill other fish/female bettas defending "their" territory, so a heavily planted tank (real or silk) & many hiding spots are necessary to break up their sight lines. A 25-year betta breeder/rescuer said she had luck getting females of different colors, as they had a tendency to have maybe one that got picked on instead of all of them picking on each other by looking too similar. I had no success with that, but you may. They will get along better if you get them from the same breeder & they've been raised together-there generally aren't those territorial issues or they're normal not so severe.

Fights, chasing & nips to establish a hierarchy are normal, but if it gets out-of-hand you need to remove the aggressor or the one that's most picked on. Beware of any behavior that looks dangerous or life-threatening to others & have a back-up plan if the sorority doesn't work out. Also, if you remove or add any they'll start fighting again to reestablish their hierachy & it may not be the same hierachy as before. Any time you add any, take them all out & out them all back in @ the same time. And some people say that small females aren't aggressive, but my biggest female was a whopping 1.2"-the rest were under 1"-& it didn't affect their aggression @ all.

The tank will need to be fishless cycled, so the girls you have now would need a temporary, heated home while it cycles if you have the bettas now & I'd really recommend waiting to get tthe rest until the tank is completely cycled. which usually takes 4-8 weeks. 0.25 ppm ammonia can kill a fish, and during cycling the levels can peak at 8 ppm which would likely kill them. Here's more info.: http://www.myfishtank.net/articles/fishl%E2%80%A6

You need:

filter (not undergravel)

filter cartridge

heater: 100 watt for a 10 gallon tank

gravel

water conditioner (needs to remove chlorine, chloramines, heavy metals. AquaClear (WalMart, PetSmart) or Prime & Novaquel (PetSmart) used together are good.

pure ammonia (@ hardware stores)

gravel vacuum

decor (do the pantyhose test and run a pair over plants or decor-inside and out. Places where they snag are also places where fins will snag, so file them down.

plants (real or silk-plastic snag fins)

eye dropper

hood/lid/cover

water test kit-liquid only. The strip tests are more $ over time and are notoriously inaccurate. You can get "Master Test Kits" here: http://www.walmart.com/ip/Tetra-Laborett%E2%80%A6

light (optional)

seeding material.

For seeding, you can use his food, a few handfuls of gravel from an established tank put them in the end of a pair of pantyhose and left on the gravel in his tank or a filter cartridge from an already-established tank.

For maintenance once the tank's cycled, you'll change 10-25% of the water and vaccum 1/3 of the gravel 1x/week (exact levels will be determined by your water test kit). Make sure to not change too much water or vacuuming too much gravel because it can cause a mini-cycle.

You could also divide a cycled tank 10+ gallons so each girl has their own section if worse comes to worse & the sorority is clearly not going to work as planned. That would only give 2 gallons/betta, which is under the preferred size; however, if it's between that & them killing each other this would obviously be the better option.

Only 1 Betta. To be honest females need 5 gallons plus. They are more active as they're not hampered by long and unnatural fins.

Females need to be kept either singly or in groups of 5+. In a pair one will dominate the other, in a trio two will gang up on one. For a proper group you need over 10 gallons, densely planted. They set up a strict hierarchy.

You should only put 1 female betta in your tank.

get 1 male and 1 female. i don't think the tank would be big enough for 3 as they like to have space to swim.