Keep a deep sand bed, preferably 1.5-2 inches. These guys constantly sift through sand to eat copepods. You're going to want to seed your tank with some pods if you haven't already. I would recommend Tisbe pods since they reproduce the fastest and are more benthic (bottom dwelling) than the other species. Dose phyto to maintain the pod population. Also feed a frozen food maybe once a day. My blue dot sleeper goby likes frozen spirulina brine shrimp. Since you bought it as a juvenile, it most likely won't grow past 3 inches because of the size of the tank. Gobies can live up to 5 years or even longer though, so if you do ever upgrade to a larger tank in that time it will grow to its full size