I had a similar question in my thread, but my tank isn't nearly as big as yours (just 24 gallons).
All the online sources say you need a ton of snails/crabs. For example, reefcleaners.org has a 55 Gallon Quick Crew package that has 71 cerith snails, 21 nassarius snails, and 28 nerite snails, and customers online are always saying that reefcleaners often sends many, many extras! That seems like an excessive amount of snails unless your tank has so much algae you can't see into it.
I've also heard per snail per gallon is a general rule to follow, but for nassarius it's one nassarius per 5-7 gallons (with 3" sandbed). I'll be good to get a more experienced person's view on it.
24 Gallon Cardiff AIO
120W Bridgelux LEDs