Hi Ghost,
There is no standard "rule" about cleaners. I have ~10 nasarius snails in my sand, ~10 margarite snals on my glass, ~6 more turbos, ~6 red hermits and 2 blue hermits, ~4 emerald crabs, a cleaner shrimp, a coral banded shrimp and a pepermint shrimp. Now, I give approximate numbers becasue I know a few have died. That's the problem with cleaners. they start small and some grow while some die. This will be something you work on for the life of your tank. Start with a few nasarius and margarite snail once your tank is basically cycled and stable. You can then add a few hermits and nasarius. After this just monitor your algae and adjust accordingly. You really can't have too many, but it's better to add slowly so you have a general count. As they die you will probably want to remove the old shells. Not that they are a problem, they are just garbage.
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46 Gal bowfront - 350W MH - 65W PC Actinic -CS90 Skimmer - SQWD with locline outputs - 18G refugium RDP- 1/4 HP chiller - 2x96W PCs on sump a fuge for coral frags and macro.
It's an overcrowded home with a little of everything and 5 fish. Thank good the fuge and sump were built for something bigger. | 
