I'm converting my 25g fw aquarium to fish only sw. I have a Penguin 170 power filter now. I'm going to buy the RedSea Prizm protein skimmer with the upgrade kit for it, Arag-Alive sand, and live rock (I haven't decided on fish yet). I have two local fish stores and one said the Penguin+Prizm would by sufficient, while the other told me just the Prizm will do. What are your opinions? Also, I'm not sure how to go about converting. Can I leave the gravel that is there and pour sand over it? Do I start with the water and sand, and then add pieces of rock slowly, or all at once? Should I replace all the water, or just add salt? I think that's all the questions I have for now, sorry for so many of them! I just want to start out right.