Join Date: Jul 2012
Location: South Eastern Pennsylvania
I don't know if you could do it with water and fish inside, but there is a method with report binders and plastic craft mesh. I think that you could go down to 2.5 gal for each betta, but no smaller.
As an alternative you could get something like a kritter keeper (I think the largest one is ~ 3 gal) and keep the new betta in there...with a heater of course.