There are an assortment of variations to the process. Yes ! They do work. I worked with at least 5 such systems in the mid to late 80's. The simplest being low flow high porosity media. The more complex being percolated, and fed metered lactic compounds. The latter being very volatile (occasionally becoming toxic due to excess sulfides) when dosing became erratic.

The most efficient systems were so maitenance prone that they quickly became unproductive. Yes, They do work, but it's Alot Like re-bristling a tooth brush.

These systems are only advantageous for dealing with Extreme Levels of Nitrates. Such as industrial applications IE: Power Plants

Most hobbiest could easily double their success with half as much work, and far less investment. Water changes come to mind...

Most of us accomplish this daily with sufficient planting, Good light and adequate Co2.

I DO Loath Naysayers, and I wish you all the success in the world ! Myself ??? I tried them out personally. They were alot of work for underwhelming results.

Given a choice I might just as well pay a friend to shoot me in the foot...?
Economically more efficient, and ultimately less painful !

I do still utilize high porosity media in low flow filters. If it works...Fine ! If not I won't sweat the details. Honestly my nitrates seldom exceed 12 ppm. so something must be working ?

Just to be clear on this both of the Seachem products do work to varying degrees. In my opinion they are good products, but be wary of other exotic systems making outrageous claims. Those that have the greatest success with them tend to focus myopically on individual details of chemistry, instead of respecting a broader scope of balance. Mi Dos Centavos, Prof M