Biological ball that is made of plastic is hollow sphere. It has large surface and can attach large sums of nitrifying bacteria. <br />It doesn't produce resistance when water is flowing among it. Hollow structure can divide water into small trickles and crush chunks of dirt. <br />Nice filter effect, light weight and portable<br />It not only can be used in biological filtration system of sea water, but also in that of fresh water.<br />Name: biological ball<br />Model: Bio-S*10<br />Color: black<br />Material: plastic<br />Diameter: about 3 cm<br />Suitable for fish pond, fish tank<br />10 x Biological  ball<br /><img src="http://img6.eachbuyer.com/x19/p76/bh688_1.jpg" / noproxy>                                                        <img src="http://img6.eachbuyer.com/x19/p76/bh688_2.jpg" / noproxy>                                                        <img src="http://img6.eachbuyer.com/x19/p76/bh688_3.jpg" / noproxy>