Includes two ¼ inch acrylic walls, 6 x 11.78 inches to install inside a fish tank to make easy hermit crab freshwater and saltwater pools - must purchase Silicone Separately Ease your hermit crab maintenance by installing pools large enough for a water filter and sturdy enough that crabs can't knock over. Perfectly sized to fit Aqueon 20 gallon (tall and long) tanks, Aqueon 29 and 55 gallon tanks. Will no't fit Topfin tanks. Use 100% silicone to install in a tank, allow time to cure, add sponge filters, decor and water Make pools as large as you want! 4 inch pools will hold .7 gallons of water while 7 inch wide pools will hold 1.9 gallons.