bro, just a suggestion, u could remove ur bioballs... i was facing very very high nitrate problems when another reefer recommend me to remove my bioballs, it helped alot as deritus will get stuck in there.
from bio balls i switched to live rock in sump. again after awhile deritus start to accumilate and nitrate went up again.
eventhough running the sump bare wont get u zero nitrates, it will help reducing them
btw ur tank is huge...nice
HTHs