I run carbon nearly 24/7 also, and change it every 3-4 weeks. I run ROX carbon in a mesh media bag between baffles in my sump. Using a reactor isn't a requirement if kept in an area with good flow. I also run GFO this way, but only as needed if determined by testing or observation.
I would worry more about HLLE than trace element depletion, especially if doing regular water changes. Be sure to rinse your carbon very well to remove as much of the fine particles as possible. There have been some studies potentially linking it to HLLE in fish. So, rinse it very well prior to use. I rinse in RO/DI water. IMO, rinsing in tap water is cleaning the rinse water and wasting some of the carbon's potential. Using a few small containers for the RO/DI minimizes waste of water when rinsing, and minimizes waste of carbon's effectiveness. JMTC & GL