The problem with a filter in SW (especially on a reef tank) is that it is too good at what it does. It turns ammonia and nitrites into nitrates quickly. That's good for a freshwater tank, but in SW you're trying to keep the nitrates as low as possible (especially a reef tank). So instead of having a biowheel or whatever making extra nitrates, you have the live rock and water changes to take out the little nitrates that you do get.
With a 30g you might also look into a good protein skimmer, to take out even more nitrates. Avoid sea clones... never heard anything good about them. I know a lot of people also don't like the prizm skimmers, but that's what I've got and it does work well. It is finicky when you turn it on but does well taking out the nitrates on a relatively small tank (I think they're insane to rate it at 90g but it keeps my nitrates very low in a 45g).