I have two bettas I bought at the same time; one in a 10 gallon and one a 2.5 gallon, and after a year of noticing how much less active the betta in the small tank is, I'm pretty convinced that 2.5 isn't enough space, especially if there are plants/decorations, etc. My 10 gal betta really seems to flourish - he moves around much more and occasionally chases or flares at the tetras in his tank. However, my 2.5 betta never flares and the only time I see him swimming around is in the mornings when the sun comes out.
I feel like a 2.5 isn't *bad*, but I don't think it's enough space for bettas to really thrive. I'm planning on moving mine into a 5 gallon within a month.
Last edited by Akuinnen; 06-19-2013 at 12:31 PM.