I used to raise Bettas when I was in my teens. I used a 10 gallon tank. I had a turtle bowl inside the tank to house the female and the male was in the 10 gallon. This way the male could see the female to get enticed but could not get to her. This also encouraged him to build the nest. Then I placed the female in with him until she laid the eggs, then she was returned back into her bowl. The water was only about 4 or 5 inches deep, (lower than the top of the bowl)thats all that is needed.