I started my 30 gallon tank off with about 30 lbs of baserock and added about 10 lbs of LR. Overtime, things changed, and I drilled the tank and added a sump/refugium to the whole system. The baserock is starting to look more and more like LR, and my system has been quite successful for a newbie like me
. All of my fish are doing great, and my corals are all growing and doing quite well.
A refugium isn't needed on a tank. Quite a few people run very successful tanks without them. However, in my case, I wanted one for extra nutrient export via growing macro algae in my refugium because I felt that my skimmer wasn't cutting it. I also assume that the extra rock I put in there also helps with additional filtration in my tank and allows me to keep less rock in the main display area... which allows for my swimming room and more room for coral growth.
-Rich