Bio wheels will contribute to nitrates, and detritus. just before a water change take a small pump and blow around the tank to get all of the detritus off of and from between the rocks, corals, etc like a storm. once in suspension let the filters do their job, then clean filters and change water. it will take a while to get the nitrates down but, it you blow around each week for a few weeks and then every other week for a couple months, and then monthly conbined with water changes you should get a better handle on the nitrates. you have nitrates because the bio load, fish, animals, feeding etc exceed the capability of the maintenance. good luck let us know how you do with the clean up.