I can't seem to keep my red cambomba rooted. My rainbow shark digs it up when he grazes the plant for algae. As this is a 6 inch fully grown rainbow, he uproots the plant with ease. Is there any way I can anchor the plant to the substrate while it roots itself? Strangely the green cambomba has no trouble rooting itself and neither do my other plants. This problem is exclusive to the red cambomba which keeps getting dug up every day. I would rather not use lead weights due to the acidity of my water.