The Juwel Nitrate Removal Sponge contains bacteria, which will after a while reduce the nitrate level in the aquarium significantly. Having removed the nitrates, which is the nutrient for the algae, they will starve or not even start to develop of this in turn will enhance the vitality of fish and plants. Using the Juwel Nitrate Removal Sponge can mean that the partial exchange of the aquarium water can be extended to 4 weekly intervals.In order to allow a proper level of micro-organisms in the filtration system it is recommended to exchange the sponge every 6 weeks.Suitable for the Juwel filter systems:+ Compact, Compact H, Compact Super, Bioflow Super, Bioflow 3.0+ Standard, Standard H, Bioflow 6.0+ Bioflow 8.0, JumboPlease choose the correct one for your filter.