I believe the concensus is, don't waste money on filtration devices that are only gong to cause you more maintenance than needed. I as well as many others, I use the this method. I still get strange looks in LFS
when I tell them that I use no filtration other than LR
In a 30 gallon tank, you are going to have more fluctuations in water parameters than say, in the larger tanks, so be careful and test often. Also, water changes are going to be more frequent. at least 45 lbs of live rock should be sufficient and a 20lb bag of special grade reef sand (sand does not have to be very deep) should be good. A good skimmer just as mentioned, will provide the means of getting the DOC
's out of the water. So in essence, your Live Rock will be the filter.. The best money can buy....