Just have to say- embarrassing though it might be, put the cause in the first post. Every failure is a chance for someone else to learn from your mistakes. Don’t leave us hanging
When you say fake rock, what do you mean? Like artificial reef rock, mined dry rock, something else etc.? Just want to get the facts here before all the chime in’s. If you have good quality porous rocks then I would contend your rocks should be in a better state after a die off than before (unless you let them dry out). In other words, more ammonia and more nitrite should induce nitrifying bacteria to reproduce and scale up to deal with it, improving your bio filter overall.
Also just curious for some more details. How old was the tank? Sand? Clean up crew? Assuming you tested, what numbers did you get for ammonia and nitrates?
Just asking because with a well established tank with a good bio filter it’s slightly unusual to hear about a huge tank destroying ammonia spike, and fish can tolerate pretty high nitrates without suddenly killing over. Did you like accidentally drop a whole bottle of flakes in a nano tank, or is this maybe a young tank?