Welcome to the site!
I think that taking out your UGF has disturbed your bacteria.
You'll need to do some larger water changes (more like 60%) to get that ammonia down, and keep adding the Ammo-Lock until things are better. Try to keep both ammonia and nitrites down below 1ppm.
Do you have any idea what cause the pH crash? Had you been doing regular cleaning/water changes until that happened?