haha thats why i hate pet store people, they always steer new hobbyists in the wrong direction and set you up for failure right away. if anything, with out live rock you would need a skimmer MORE but honostly, i would deffinitly get some live rock and a skimmer. i used to have just sand and a skimmer and fish would die left and right which sucks with SW fish prices but once i put the live rock in there about two years ago i have not had one fish ever get sick, although some little guys dissapear once in a while since ive converted to reef. but yeah if you just wanna go with all fish i would still definitly recomend a good amount of live rock----you wont regret it----and besides it looks cool too