Wrasses come in a variety of sizes and dispositions. Some are reef safe, while others may not be. Some wrasses are very helpful in a reef aquarium for getting rid of pests. A sand substrate should be used if wrasses are to be kept, as many will like to bury themselves while they rest, or when they are afraid of something in the aquarium and need a hiding place. It is not uncommon for wrasses to disappear for a day or two as they hide, but these fish are usually very visible and active.