Even that part is variable
The only way to know what type of work will be needed is to pick some up, drop it down in the tank water and see if it clouds
If it does, that's the bad stuff he's talking about
Because my system is small it can be treated lazily then rip cleaned to new
A 180 gallon sandbed in contrast should not be allowed to store or catch-up will take years not minutes as mine does to rinse the bowl out
can say in good faith that the more gallons of water I kept or the more rocks I stacked on sand to make me not want to access it, the less deep I'd have a sandbed and would be at no sandbed in a display tank anywhere above a forty gallon setup because I'd be too lazy to keep it clean.
Since I know the key to indefinite biological lifespan in a reef aquarium is not storing up detritus, out of sight is never out of mind for me. A sandbed literally has to pass a drop test or I will feel like I just put my dinner plate up under my bed so that it can't be seen and could call the house clean because it looks nice topically just don't go poking around