Yes, we use the same filter in both freshwater aquaria and saltwater aquaria. You are probably wondering why. Well, the bacteria in a saltwater aquarium system are different from the bacteria in a freshwater aquarium. The filter works just fine for both. There are other differences between a saltwater aquarium and a freshwater aquarium. A freshwater aquarium is different from a saltwater aquarium because there are different fish in each. So what kind of fish? Some fish that you don't see in a freshwater aquarium but you may see in a saltwater aquarium are clownfish, damsels, and tangs. These are fish that are a little more difficult to take care of because they need a specific temperature and a specific level of salt in the water. Take care of the fish and you will be rewarded.