Live rock is the most common filter for SW
tanks. A protein skimmer (saw your other post) helps remove some excess crud too.
The key to live rock for filtration is LOTS of circulation, at least 10 x per hour turnover, up to 20 x per hour. You'll probably need 2-3 large powerheads, plus the return from your sump pump to reach the right levels of circulation.
This helps large detris break-up so it can be removed via skimming and the live rock filtration.
Water changes should remove the rest.