There are so many opinions on this topic that you're going to get a million responses. Everyone has one that works for them and many that haven't. I've owned 8 different skimmers and my favorite by far is the Lifereef skimmer. It's $419 without a pump for a brand new one which I know is slightly above your 400 limit, but you can get them used on reef2reef for less than that. If you buy it new or used, Jeff from www.lifereef.com stands behind them, hand builds them, and will answer any email you send him practically the same day. They work with any pump that meets the min flow rate and can be upgraded at any time with larger pumps or add on sections to make them work for larger tanks. Talk to Jeff and see what he recommends. You will not be disappointed, nor will you ever buy another skimmer which will save you money in the long run. I don't even want to know how many thousands of dollars I've wasted on skimmers. Argh... Good luck.