I run Carbon 24/7 in My SW Reef and once a month in my other tanks. I regularly put my hand in the reef tank and the soft corals tend to send out chemicals as a defence mechanism. That is why I run it 24/7.
IMO a good filtration system must have all 3 (Chemical, Biological, and Mechanical) Mechanical includes water changes!
Oh, and be sure to ONLY use a premium quality carbon. I use 2 Little Fishes Hydrocarbon.