I set up my tank using the Miracle Mud refugium system. I somehow talked myself into spending $70 for 10 lb of dirt. I think it was a good decision. Regular silica playsand is not what you want in a marine tank. You want sand from crushed coral made of calcium. If you plan for mud in a sump in order to grow macroalgae then the dirt adds greatly to the success. Walt Smith also markets mud from Fuji which recreates the mangrove forest bottom, an environment which is the nursery to many sea creatures.