probably just an ammonia spike, did you test it at that time?
what your trying to do is build up bacteria, cleaning it will only prolong the process by taking it out.
...when most people say water change they are referring to gravel vac, sorry i thought that was what you meant for some reason.
hmmm. i'm not entirely sure then. you have biological media filters(ceramic rings etc.) in your filter right? do you have sand or gravel?
sounds like it should all be going away soon(id say within like a week) your spike seems to be done and your nitrites are dropping off. maybe your just finishing and your cycle took that long for whatever reason...