There are a few ways to determine if your filtration system is working effectively. First, observe the water clarity. If the water appears clear and free of debris, it's a good sign that the mechanical filtration is doing its job. Additionally, monitor the water parameters regularly using a test kit. Low levels of ammonia and nitrites and stable nitrates indicate that the biological filtration is working effectively. Another way to assess the filtration system is by observing your red-eared slider's behavior and overall health. If your turtle is active, has a healthy appetite, and its shell looks clean and free of any abnormalities, it's likely that the filtration system is providing a suitable environment for your pet. However, if you notice any signs of illness, such as lethargy, loss of appetite, or shell discoloration, it could be an indication that the filtration system needs adjustments or maintenance.