Sulfur Pearls are beads formed from pure sulphur. They are used in sulphur nitrate reactors as the filter medium and energy source for the bacteria. They have to be replaced from time to time as they are slowly consumed by the bacteria. Caution: Use only in nitrate removing anaerobic filters having a low water flow rate. The pH value and carbonate hardness (alkalinity) of the aquarium must be monitored regularly. We recommend sulphur filters are only used only in combination with a hardness reactor, filled with Hydrocarbonate, to neutralize the acid produced.