I just did a partial water change on my 10 gallon tank. After doing that, I was really annoyed because even after that work the water still looks really dirty. It has brown poo floating around and a few leftover pieces of bloodworms. Is the filter not doing it's job? It's a 5-15 gallon whisper filter, and it was brand new a few weeks ago, so it should be fine. What is the problem?