Definitely use the reactor for GFO! Even if you had no problem, it wouldn't ever hurt to run one. With the levels you report in this case, you "should" run one. To help the situation more than just weekly water changes or skimming(with trying to export) and other import issues/food/waste breakdown etc.. which can make even very low levels- often grow undesirable stuff. Or effect some lifeforms(corals) Even when some tests say very little to no phosphate...
The reactors in most peoples cases are still warranted equipment, well worth having regardless of levels.
I agree with others saying here about it and the style- No offense but the "Dual" sucks. Either get a single or better yet, Mod it to be single like Tonynlo did. It will run better. Sometimes companies produce things trying to be more efficient or market them in a way to solve multiple problems in one unit. It cost more than a single but less than 2 singles getting the same job done. That's the thought- more for your money. BUT the problem is it doesn't work good using both GFO and carbon in a dual. One especially- carbon always gets messed up quicker and screws things up. As well as the pump efficiency is down, on how it actually lets the dual perform both.
So, long story short, just run GFO in a single. It works best.
Granulated Ferric Oxide(GFO) tumbled properly is essential.
(IMO) Carbon is a great polisher everyone should use to varying certain degrees depending on their particular tank. BUT not as important "tumbled" as GFO is. You'd be OK like most (IMO) just running some Carbon in a filter bag in a general flow area and changed at least monthly. Don't use too much either. Carbon however good, can also be over used and cause some less commonly seen negative effects. (perhaps on some fish species) Less is more with Carbon.
GFO is King.
