Amazon has the Aquaclear 20-Gallon Foam Inserts, 3-Pack for $0.98.
https://www.amazon.com/gp/product…=UTF8
Amazon also has the Aquaclear 30-Gallon Foam Inserts, 3-Pack for $1.40.
https://www.amazon.com/gp/product…=UTF8
Amazon has the Aquaclear 20-Gallon Foam Inserts, 3-Pack for $0.98.
https://www.amazon.com/gp/product…=UTF8
Amazon also has the Aquaclear 30-Gallon Foam Inserts, 3-Pack for $1.40.
https://www.amazon.com/gp/product…=UTF8