This Fish Tank Biochemical Filter Sponge can be used in sea water tank, fresh water tank, aqua-plant tank. The size can be cut freely as you need. Thickening Biochemical Filter Sponge, tough and durable. Good shading features, can reduce the algae breeding. Moderately hole, can cultivate high density nitrifying bacteria. Feature - Color: Black. - Material: Cotton. - Size: 50x50x2cm. - This Fish Tank Biochemical Filter Sponge can be used in sea water tank, fresh water tank, aqua-plant tank. -The size can be cut freely as you need. - Thickening Biochemical Filter Sponge, tough and durable. - Good shading features, can reduce the algae breeding. - Moderately hole, can cultivate high density nitrifying bacteria. - Warm Tip: Dear buyer, due to lighting effect, monitor's brightness, manual measurement, etc., there could be some slight differences in the color and size between the photo and the actual item. Sincerely hope that you can understand Thank you