Others may disagree, but I don't think removing the biowheel is going to reduce your nitrates. Ammonia is converted to nitrite which is in turn converted to nitrate by oxygen loving bacteria. Nitrate can be converted to nitrogen which will escape to the atmosphere by oxygen hating bacteria if you have an anoxic (no or low oxygen) zone of sufficient space int he aquarium such as a deep sand bed, the interior of live rock, or a nitrate reactor. Simply eliminating one area that is oxygen rich (like the biowheel) doesn't create an area that is oxygen poor.
(I'm going on a little rant here.) I know a lot of people say that wet / dry filters (and a biowheel is one form of a wet / dry) are nitrate factories, but the nitrate comes from the nitrite which came from ammonia which came from the fish. I don't see how a wet / dry increases the gross amount of nitrate produced. All things being equal, the same amount of raw material (fish waste) is going in, so a proportional amount of nitrate is being produced in the system. You can change what happens to that nitrate such as export via water changes, use by plants and animals as food, processing into nitrogen by anoxic bacteria; but that seems largely independent of how the nitrate was produced to begin with. (OK, I'm off my soapbox now.)
Nitrates can build up if you have an accumulation of detritus due to a dead spot or in a mechanical filter. They can also result from over feeding or lack of partial water changes and sometime through the use of a water source for top offs and water changes that already has nitrate in it. This is why most reefkeepers use RODI
How do you make your top off water or your fresh saltwater for water changes?
How often and how much do you feed?
How often do you do water changes? How big are they?
The answers to all these questions will help to determine the source of your nitrate problem and will help you be able to manage it.
You indicated you had 7 medium / large pieces of live rock. How much does that weigh? (The general guideline is 1 to 1.5 pounds per gallon. Therefore, you'd want somewhere between 30 and 45 pounds of live and or base rock in your system.)