You're changing an awful lot of variables all at once, so your readings (and your nitrogen cycle) are likely way off. Slow down a bit, and let's look at the possibilities one at a time.
First, most water treatments that neutralize ammonia work by converting the ammonia (NH3) into harmless ammonium (NH4+), which will by removed by your bio filters. The test kits can't tell the difference, giving you false positives. Similar story for chlorine and chloramine treatments. You shouldn't take water readings too shortly after making water or chemistry changes. You have to give it a day or so for the water chemistry and readings to stabilize; otherwise, you'll be chasing thrashing readings and probably making things progressively worse.
Most of the beneficial bacteria that remove these compounds lives in your filter media and your substrate. When doing your partial water changes, you should only siphon off the surface debris and only "deep clean" about a third of your gravel in any given week (max). Also, changing your filter material can cause an ammonia spike because you're throwing away the "bio" part of your bio filter which stalls your nitrogen cycle. You should only rinse your filter media in aquarium water (not replace) and only when needed. I only replace individual pieces of my filter media when it is absolutely falling apart (try not to do too much at once).
I'm not sure if you've determined that you need all those other chemicals you're adding during routine water changes, but in general… stop adding any chemicals that you don't explicitly need — i.e. you need a water conditioner but really not much else unless you have diagnosed a specific condition that needs treatment. I'm assuming your tap water is basically okay with the chemicals you are using, but you may want to take a fresh sample to your local aquarium shop for a test to see what you actually need.
