i have a 120 gallon reef that is about ready for some clean up. What would be a good recommendation for the quantity. Saltwaterfish.com has a 70 quantity of crabs and snails but just wandering if that is enough?
I'm not sure such ratios are particularly helpful because in the long run your challenge is to find the right number and types of CUC members making sure there is enough food for them, recognizing that different types of snails, crabs, etc. eat different types of detritus, algae, etc; some CUC aerate the sand while others pretty much clean glass and rocks; some will "steal" food from your corals and become pests in that sense; and so forth. These considerations certainly complicate your selection, but you want to avoid having some CUC members from starving to death and others becoming a nuisance (some reefers put emerald crabs in this category for instance).
Moreover, all reef tanks are not equal. For example you may have high levels of nutrients and the resulting algae, requiring more snails than you would if you run a low nutrient type of tank. The key, of course, is to match supply with demand and preference.
I would start slowly and add those types and numbers of CUC necessary to keep your tank healthy and entertaining, just like you'll do when deciding to add a new fish or coral. For me, this is part of the fun to learn about inverts' habits, preferences, utility, etc.
Liveaquaria.com also has some reef cleaning packs which provide some ideas for what you might want to consider in terms of different types of inverts, etc.:
http://www.liveaquaria.com/category/2732/pacific-prebuilt-reef-cleaner-packages?c=420+2732
Good luck.
