I'd love to see some pictures!
My betta just swam quickly towards a guppie when I put one in with him, then just as quickly swam away and stayed on the opposite end of the tank. No harm done. I imagine as long as there's ample space he won't be too stressed.
They thought Noah was crazy when he built the ark.
They thought the forefathers of America were crazy when they rebelled.
They thought Howard Hughes was crazy when he built the Spruce Goose.
OK, Howard Hughes was crazy. But hopefully I'm not. :)