Usually, people buy way too many CUC for the size of their tank.
Me, for example. My CUC is too many, but I have no issues with algae or uneaten food. MY CUC for a 34g tank consist of:
-tons of dwarf ceriths (well, about 30) they are great with sifting sand and they're not bothered by my hermit crabs
-3 cerith snails (like the above, but bigger) I used to have more but my crabs like their shells...
-5 nerite snails- algae eating machines and they look cool too. They don't grow quickly, the only bad thing about them is that they lay eggs everywhere and you have to have a cover with them, they like carpet surfing
-6 hermit crabs- I wanted to get rid of them because they knock off frags sometimes, but they are so comical in their appearance that I decided to keep them. Make sure you'll get the small ones
-5 astrea snails- again, they are very good with eating algae, but you have to watch them as they can't straight themselves up when they land on their shells
-one small serpent starfish- this animal is so entertaining to watch and it can squeeze everywhere for leftover pieces of food
-2 cleaner shrimps- what can I say, they're great with eating leftovers and cleaning fish, but the problem with them is that they are eating like pigs so when I'm trying to feed my LPS I have to constantly watch cleaner shrimps- you turn your head in other direction for a seconfd and here they are stealing food from the coral