There are a ton of articles on how to convert an AquaClear filter into a refugium over at nanoreef.com . Some are fairly simple while others get quite involved. I kept it simple myslelf and just shaved the impeller of a old AC500 (new model 110 now) and added some baffling to keep the chaeto in. Whatever you use its best to reduce the flow by modifying the impeller. The AquaClears are popular since they have a nice rectangular shape and are easy to cut and glue. Its also easy to attach a light fixture to if needed.