Glass Bottle Fish Bowl
Keep your small fish in a glass bottle! Find a large glass bottle or vase and soak the inside of the bottle with warm water several times to clean any residue. Cut the top off the top of the bottle just below the neck. Pour gravel or pebbles into the bottle and bury the roots of a tall living plant in the gravel. Fill the bottle with water prepared for your fish and set the top of the bottle on the base.
I really hope that nobody tries this. Betta Splendens naturally live in 4ft of water with large territories. They also need to breathe air, which living in a bottle makes quite difficult.
They need filters and heaters. They are intelligent fish who need lots of stimulation.
To keep one in such poor living conditions is to neglect one.
Don’t believe me? Research.