These filters have fallen out of favor with reef aquarium hobbyist because the bio-balls leach Nitrates into the aquarium water. The protein skimmers found on these types of filters are not very efficient either, and when used in a reef aquarium, they do not remove organics fast enough to keep phosphates and Nitrates at the levels they need to be.
These filters are very efficient at removing ammonia from the water and, thus, are a good option if you're creating a fish-only aquarium. One problem with wet-dry/trickle filters occurs during their transformation of ammonia to Nitrite and then to Nitrate. In a reef aquarium, these compounds are dangerous to the sensitive corals and invertebrates and, thus, must be removed. However, the wet-dry filter is not capable of completing the nitrogen cycle and, in fact, adds to the Nitrate load of the tank.
We do not recommend using these filters for reef aquariums.
