https://reefs.com/sulfur-nitrate-re...plement,the reactor, under anoxic conditions.
“During the cycling period, it’s important to adjust the flow rate through the reactor, usually between three drops of output per second, down to one drop of output per second.”
I have never used a sulfur reactor to control nitrate as I used a Jaubert Plenum for > 20 years. Now I don’t need to reduce nitrate and in fact, I dose ammonia.
I was curious about the chemistry so I googled it. I made a DIY calcium reactor which has similar function. I don’t see the need for a closed loop. Reduced flow thru the sulfur media consumes oxygen and grows anaerobic/Faculative bacteria which in turn scavenge oxygen from NO3 molecule and release a nitrogen gas molecules.