Advise from rox carbon users please.

[Willito]

IME, ROX carbon is a powerful absorbant and very effective at soaking up pollutants. It does wonders for the reef if you use it properly. I've been using for a few years in a mesh bag hovering just above my return pump. The trick is to massage and rinse the bag once a week under tap water. This will wash away bacteria and build-ups that bonds to the bag and carbon and inhibiting it from peak performance. I use roughly 100ml on my 120g system and change it out every two weeks. IMO, unless your system is 180g or bigger, using such small amount it in a reactor is overkill.