Water cabbage adds green to the water body. It absorbs the food waste that we feed the fishes to grow rapidly. It helps clean the water. But when it grows too much, it starts blocking sunlight to water and makes the fish tank system go unbalanced. Hence, we collect it once in a while and use it as an organic fertilizer for our other plants. Also, leaving a bunch of these around a plant gives cool roots and provides fish-based nutrients as fertilizer. See more at www.frogsandcashews.com or on YouTube.