Here is my 2 cents.
When algae starts to grow on glass and surfaces, add a few Snails. Add more Snails at intervals as the algae becomes more than the Snail population at that point can eat. I believe something is said about this in the Reefkeeping Tips.
There is also a helpful thread linked there about the best Snails.
Hermit Crabs are not as critical as Snails and can cause problems if too many are added.
I don't think of Shrimp as part of the CUC.
There is a crab, the Valonia eating Emerald Crab (Mythrax Crab) which can be useful if and when Valonia(green Bubble algae) start to show up.
The best animal, IMO, to keep sand looking clean is the Sand Sifting Cucumber(Sea Slug). They come in a variety of colors. They are best added after 6 months or so, otherwise they might starve.
While we're on the subject, I do not recommend Sand Sifting Stars. They eat the beneficial bugs and worms that can grow in the sand that are food for coral.
Aloha,
Mark
Edited by Mark Peterson - February 22 2016 at 4:23am