I just set up this 20 gallon long (30”x13”x13”), upgrading from my 10 gallon tank I had before. I currently have about 20 pounds of liferock and a pretty deep sand bed (2”-4”). I have a chalk bass and a tangaroa goby and 3 blue leg hermits that I moved from the 10 gallon. Any suggestions on what I can add? I would like to add more inverts and another small fish or 2.