my ORP jumped 100 points in two days

[truperc]

I know ORP isn't the most important variable to test but after putting in a cup of Reef Crest ROX carbon into my 175gal tank my ORP has climbed steadily from 300 to 400. My level has been lower as of late but I have not had levels above 360 since I set up my apex in January. The only other maintenance items I did was change my GFO, clean my skimmer cup, clean my filter sock and harvest some cheato.

I can't find anywhere that carbon would raise ORP?

Any ideas why this would be happening? Should I be concerned?

Thanks