Something natural, not little bits of meat pushed together that didn't make the cut for USDA standards.....
Try getting 2 unseasoned raw jumbo shrimp from your local grocery store and stick those in a zip-loc bag, poke holes in the bag and stick it in the tank. Monitor the ammonia, nitrites, and nitrates. Don't use the other tests as most of those params will be all over the place during the cycle. Watch for ammonia to turn to nitrites and as soon as there are no nitrites, your cycle is basically completed.