Rule of thumb for per gallon clean up crew

[Ronny#66]

I have 25 gal have about 12 various crabs and 6-7 snails would like to add a few more snails . few more crabs what do you advise ?

[coast2coast7390]

what type of snails and crabs

[Skier1]

I'd recommend buying the new book "Reef Invertebrates" by Fenner and Calfo. Nice section on snails with specific recommendations by type. Plus other great info on other invertebrates as well.