Also, because of how low the water levels are in the tank, the muffler helps to keep the flow of incoming gunk from being interrupted. If the water flows out of the filter and directly into the water in front of it, it works to defeat its own purpose. Warmth is a key part of my water tanks. You might want to put some sort of hide in there, as well. Dsmalex's plants are a good idea that gives the frog a bit of cover.