The Fluval A1378 is the correct replacement filter for the following:
The Fluval A1378 - Fluval Spec Biomax Media Insert is a replacement aquarium filter for Fluval Spec Aquariums. The Fluval Spec Biomax filter provides Stage 3 biological filtration for your aquarium and maintains a healthy environment for your fish. This aquarium Biomax filter has a large surface area that supports beneficial bacteria colonization.
Fluval A1378 - Fluval Spec Biomax Media Insert specifications: