I have a small uth on the cool side but on a 10 gallon, you shouldn't need it! Cover the sides and back and top with foam board and that will keep in the heat! You can get it cheap at Home Depot for like $6! Also are you measuring ground temps? Cool side temp of 80 should be the belly heat! The air temp should be at least 75! I use the foam board for the winter months! It doesn't look very pretty but it works!