Hi I set up an new tank 4 weeks ago, last week I started again due to an infestation of string algae, I had a fish in cycle going with a few zebra danio and all was great before the algae but I was keeping the ammonia levels down with pwc, before the restart I did not have any nitrites appearing, I'm just wondering how long they will take to appear as I saved the filter media so it has really been running for four weeks? Any advice greatly appreciated.