The NR400/1000 can be as effective as the surphur conterpart but u must know the working concept behind it. I connect my NR1000 with a Mv meter & control the water inlet according to the ORP. The best value is -100 to -200mV & NO3 is always reduce to 0ppm. If u let it increase to more than -50mV or even positive,no NO3 will be reduce.If it falls below -300mV,all NO3 will be reduce & the bacteria start to use sulphate! The result will be having the so call fouling rotten egg smell-Hydrogensulfide.This explain why many units failed to work & many reefers gave up eventually. Without a mV meter,its very difficult to know the situation in the denitrator itself.
Its stated in the instruction book as: If u use denimar powder,increase the feeding if the mV increase too much (more than -50mV)
If u use deniballs,decrease the flow rate to between -100 to -200mV.
I nearly gave up this equipment but after hooking up with the mV meter,it works!
I'll add a pic to explain later