As Bang said, the high amounts of ammonia or nitrates or other toxins leaking from rocks ect. will cause hitchhickers to start to die off and that will cause "more ammonia" and that will make the cycle take longer....no need to too much bacteria if your not goimg to provide that much livestock to substain it. Lack of bio-load will cause the extra bacteria to die off anyway. The cycle is to grow enough bacteria you need to put in a few fish safely and as you slowly add livestock then the bacteria will keep up. Best to feed a cycleing/cycled tank a small amount of fish food for a while to simulate haveing fish and to balance the amounts of bacteria, while doing water changes and running filters, skimmers and lights as well.