Remember, remove slowly. You've had that crushed coral substrate for a few years. There are a lot of nasties in there. 20%-25% at a time. Don't scrape it off the top. Remove one section from the surface to the bottom. Wait a week and remove another 20%-25%. Continue until it's all gone.
When adding the ESV fine shugah , make sure to add it slowly as well. It is a calcium carbonate sand and you don't want to overdose the tank with all that at once either.