The BRS Dual Reactor states the canisters can hold 3 cups of carbon and 2 cups of GFO. I'd think that would be enough for a 180, but I'm no expert on reactors.

I'm not worried. I've added a filter sock and macro algae to the sump. I think as a combination, it will do what I need. I didn't max out the amount of media I put in, if it needs more will add more but will see how things look over the next month.

Yeah I don't really see how they can have a rating either... I mean couldn't you just change the media more or less often depending on your needs? Or use more or less media to begin with.