You need to cycle it.
You can do it in a Rubbermaid tub you will need a heater and water pump. Start by removing any die off that's on the rocks. Put the rocks in the tub fill it with salt water and turn the heater and the pump on. And it will cycle just like your tank did. After the nitrogen cycle is over you can add it to your tank. If you search for cycling LR I'm sure you'll find a few threads on the boards.