I currently have a 29 gal SW tank with @40 lbs or live rock and a 3inch sand base running. There is a Magnum 250, and I have a Prism skimmer running on the tank, the basic one, which i realize is not the best, but when it runs it is barely pulling anything out. There are 5 fish in the tank, a chromis, 2 clowns and 2 damsels. I make water changes of 20% every other week. The LFS said the reason i do not appear to be pulling anything out is because of those water changes and im not giving it enough time to develop. Does this make any sense? And if so, does it make sense to still run or have a skimmer.