ReefNOOB21: As other's have said, your live rock acts as your primary filtration system. A protein skimmer is also a good addition because it will pull undissolved solid matter out of the water column, helping to keeping your water clean. You do not need a biowheel or canister filter - they are really made for freshwater. Some people with HOB filters such as the biowheel take the filter media out of them and use them strictly for flow, or to convert into a mini refugium with live rock rubble, chaeto, and a light bulb to help grow the chaeto. If you are going to use the biowheel, I would recommend going the refugium route. And with a tank your size (25g), you can probably get away without having a protein skimmer, as long as you are doing regular water changes.