definitely sounds like a minicycle, this is why its good to stuff extra media in your filter area, so that you don't take it all out at once if you have to replace something. Your water parameters will tell you whether you should be doing water changes, so test your water. ideally you want to be at 0 ammonia 0 nitrites and <20 nitrates, but slightly elevated levels of ammonia are kind of inescapable during the cycling process.