I have a standard 10 gallon tank from Petco. This didn’t fit as the top was a cm too large. I like that the Perspex / acrylic is so clear. The holes also. My Bettas get along but I like to separate them every now and then - if I’m out of the house for more than 6 hours. I’ll try and find a 20 gallon that this could work for as it’s such great quality. Most Bettas need a black wall so they can’t see each other. If you buy this tall plants can help. Or one way film.