Review on Aquapapa Bio Sponge Filter 4-Pack for Up to 10 Gal Breeding Fry Betta Shrimp Turtles Nano Fish Tank Aquarium by Becky Barlow

These little filters are great for small bowls and tanks, I would say 2.5 gallons and up. If you want to get one, you might as well get 4 and have a few on hand if you want a different betta (they're like chips, you can't just have one)! Ideal for aquariums with young fish and shrimp! You can also use them in combination with a hanging filter in any size aquarium for extra oxygenation and biological filtration. None of my bettas have ever objected to a sponge filter - it creates bubbles but keeps water out. Completely eliminates the surface film that forms on stagnant water. This size fits in the palm of my hand, about the size of a plum. Under $3 each and premier shipping from the USA, what's not to love?