I ordered this for my classic (globe shape) 8 gal Biorb. But it can't fit in the hole in the top. Then went to biorb shop website where they have a chart for each item showing which tank it fits in. You must check the chart before you buy anything for a biorb tank to be sure it fits. Now have a bigger Biorb tank and love this ornament. The ornament is a 5 but the description saying it fits an 8 gal tank is a 1.