I have a well established 75 gallon reef aquarium with a 20 gallon sump equipped with a protein skimmer and phosban reactor running. I do about a 20% water change weekly and the parameters are as follows: 1.024 salinity, 350 mg Calcium, 8.0 dKH alkalinity, 0 nitrates, 0 phosphates, 8.0 to 8.3 pH, and a temperature of 79F. There are a number of LPS corals and a blue tang, six line wrasse, 2 clown fish, 3 blue-green chromis, and a hector goby. I also have about 80 lbs of live rock and a 2 in sand bed with live sand. Their are number of snails, a few hermit crabs, 2 peppermint shrimp, an emerald crab, and at night a host of small copepods scrurry in the tank. All corals and fish seem very healthy and are growing nicely. However, I just can't seem to get rid of the brown algae in the sand (see attached picture). I vacuum it out weekly with the water change and can't figure out how to get rid of it. For a while I had a orange spotted sleeper goby that did a nice job of keeping it clean but it was burying all the coral on the sand bed. Any suggestions