I have a wet/dry filter on my 75 gallon Freshwater tank but I am very particular with how the tank looks. I want the most crystal clear water as possible. All of my readings are perfect but to me the water could be more clear so..... I am adding a Fluval 406 external to run with the Fluval Biomax Bio Rings and Fluval Carbon. I also ordered the spray bar for even better circulation. None of this add on was needed but hey why not right? If the tank is not crystal clear after I get all this in and going then it will never be!