Any bacteria bottle. Dr tims and io Bio spira seem to be pretty good. Then get ammonia from hardware store or from Dr tims. Follow the directions on the bottle or dr tims website. Pretty much, put bottled bacteria in tank and dose ammonia to 3ppm. Then wait for nitrites to show up. When ammonia gets to zero redose ammonia to 2ppm/3ppm. Keep doing this until ammonia and nitrites are reduced to zero in 24 hrs or less. There's lots of forums and websites that have detailed "fishless cycle" instructions.