Andie
Fish Addict
I'm not exactly sure if a betta would mind being covered, since I never thought to ask any of mine
Still, you'd think constant darkness wouldn't be good for anything, so try a very light piece of patterned silk, like the material for a sarong skirt, that would let light filter through. That, or maybe even a piece of lace/crocheted blanket, or similar. That way light would get in, but if you were to say sit a little clock or fake potted ivy on top of the tank, it would just look like a slightly overelaborate decoration from the outside. Residence isn't the most private place to live, so just bear that in mind when planning your setup. Where are you going to school, anyway?