Join Date: Nov 2011
Location: Yorkshire, England
Victor, my crowntail betta (as pictured in my avatar ;)) can be quite aggressive. He is currently housed in a 5 gallon (25 litre) tank with 3 platies (and 3 platy fry, which are quarantined in a separate hatchery, at least until they get big enough to not be Victor's lunch =P) and he flares at them and chases after them when they get near any of the bubble nests he makes (or tries to make, since there's a filter), or sometimes he just goes after them in general.
There are times where he flares at his reflection in the glass too, which happens more frequent once the light has been turned off. Otherwise, he has his calm moments, like right now where he is just hanging around in one of the corners.
On the other hand, Spartacus, my mum's blue crowntail betta, is quite calm with his Zebra Danio tank mates. From my experience (and it's quite short lived xP) I've always found blue bettas to be quite calm compared to red ones. My sister has a red veiltail betta, and he has already taken the eye out of one of her rummy nose tetras.