oh yeah... forgot to add that "cleaner clams" most likely won't survive for very long in the more coarse crushed coral substrates..
speaking of which... very large crushed coral substrates can be problematic (if not set up a certain way) as far as nitrates go...
what size grain is your crushed coral? If it's really coarse, it works best with 1/2 an inch or less in depth, and even then you should syphon at least weekly... probably more often if you keep trigger or other messy feeders... If you have it too deep, (over 1/2 inch) you can develop what is called "nutrient sink" where uneaten food, dying/dead algae, and fish waste will accumulate and really foul your water...