Some signs of a malfunctioning filter include:nn1. Reduced water flow or no flow at all.n2. Accumulation of debris in the tank.n3. Cloudy or foul-smelling water.n4. Poor water quality as indicated by high ammonia or nitrite levels.nnIf you notice any of these signs, inspect the filter for clogs, check the impeller, and ensure that all components are functioning properly. If the issue persists, consider replacing or repairing the filter.