For now, stopping the feeding of your fish is the best bet. Adding Stress Zyme at this point doesn't do much good for it will only create more ammonia when it converts the solid waste.

Just as a note, I recently learned that chloramines in the water (city water from the tap) show up as ammonia when using your test kit. I recently saw a post that had high ammonia from the tap. That may have been chloramine, which can only be removed via a filter designed to do just that.

Check the water you are putting into your system and, if it is clean, then you may need to do a water exchange. The ammonia is too high and if it were me, I would (and have) have done a water exchange by now in order to get the ammonia down below 1 ppm.

Oliver