Nitrates accumulation is without doubt the biggest problem in fresh and salt water aquariums.

Classic denitrificators use the metabolism of anaerobic bacteria to reduce nitrates into gaseous nitrogen. These bacteria need a regular addition of carbonated stuff (glucose, methanol etc.) and anaerobic conditions (lack of oxygen).

A more efficient solution is represented by the sulphur beads denitrificators.

Sulphur based denitrification is based upon autotrophic denitrification by sulphur-oxydizing bacteria , such as Thiobacillus denitrificans. Under anoxic conditions, these bacteria oxydize sulphur to sulphate while reducing nitrates to liberate the oxygen for their own use.

This is the chemical reaction which takes place in fresh water:
2NO2 + S + H2O + CaCO3  =   CaSO4 + N2

The process in seawater is not yet fully clear, but it seems to work with the same result: the total remove of nitrate.

The system uses small beads of elementar sulphur placed in a contact chamber (reactor). The water is flowing from the bottom to the top of the chamber at a very slow rate. As the water moves slowly upward, oxygen is utilized by Thiobacillus denitrificans, making the chamber more anaerobic the further the water rises. At this point, bacteria will use nitrate in absence of oxygen, reducing them to gaseous nitrogen, which leaves the water also thanks to the reverse-flow of the reactor.

The chemical reaction that takes place releases sulfate (1.1 mol of sulfates produced for 1.0 mol of nitrates reduced) and excess hydrogen ions, which makes the water acidic (it is believed that also some CO2 is produced, further acidifying the water). To counter the acidity, the effluent from the sulphur reactor should pass through another reactor with calcareous material (for example coral sand), in which the acidic water will dissolve the coral sand, raising the pH and generating calcium ions: in this way the drawback becomes a good advantage…….!  Also, passing the water through calcareous gravel precipitates the sulfate and prevents it from entering the aquarium.

In fish-only systems sulphur beads denitrificators can easily help bring down nitrates to much lower levels. They also help keep nitrates under control in reef aquariums where some more delicate nonphotosynthetic corals, like Dendronephthya, are kept. Furthermore, they can also help in reef systems with hard photosynthetic corals: low nitrate is essential for minimising nuisance algae and improving the coloration of corals (even in tanks with a content of 10ppm or less, this level can cause an increase in zooxanthellae and a browning of colour as the density of cells increases).

The biggest advantage of the sulphur-based denitrificators is that they do not need to be constantly adjusted and to be regularly fed with nutritive carbonated solutions like glucose, methanol or other.

As an empiric rule, 1 litre of sulphur beads is enough for 100 litres with nitrates  < 60 ppm, for 200 litres with nitrates < 40 ppm or for 300 litres with nitrates < 20 ppm.  If necessary, bigger or more sulphur beads denitrificators can be used.

Use of sulphur beads denitrificators should be limited to aquariums where the nitrification process is already working, because some NO2 and NO3 can occur from denitrificator’s outlet during starting the filter. They do not represent any risk in already balanced systems.

RW sulphur beads denitrificator are available in 2 models:
 * RWS2 – with 1 chamber for sulphur beads and 1 chamber for calcareous material
 * RWS3 – with 2 chambers for sulphur beads and 1 chamber for calcareous material