Read up on fishless cycling. It will enable you to cycle your filter without putting fish in the tank. Some people use a shrimp or prawn, dead of course or a frozen one. As it breaks down it gives off ammonia and feeds the filter. Nitrites form and then nitrates and you test for ammonia until it has got back to 0. Read up. But be patient. Over the counter bacteria don't really work and there is no quick fix.