I get some frozen raw sea food mix, we call it marinara here and put it in a bucket of fresh salt water or get it from some else’s tank, then with an air stone to rot for a week or so, then pore that buckets water through material to get particles out then add that putrid water to the aquarium as it is varied ammonias, then add either purchased bacteria or a little matured media from another aquarium and the cycle is very fast and very strong! Then do it in a smaller amount each week for three weeks after nitrites hit zero and you are done. If you do a non natural start you can get an ammonia lock and you will be waiting for months.