Wouldn't an easy growing coral, such as Xenia, GSP, or Kenya Tree be helpful for filtering in this case? The more waste the faster they grow!I'm not sure, depends on their size and species. Most likely, they would never come in contact with the sharks. Using animals to clean up after other animals does not always work - the excess food is still in the system, it just get converted to crab waste. It is better to control nutrients by careful feeding, and then, to not overload the systems with animals.
Jay