When placed in the aquarium, catappa tubes will slowly decompose, releasing tannins that turn the water yellow or brown. These tannins can lower the pH of the water and are thought to kill bacteria and fungi, which is useful for fragile fish. The dark colour of the water dampens light and mimics the natural habitat of many fish, which can help reduce stress. This is why many aquarists use bark tubes in their tanks. 1 bark tube lasts approx. 4 months. Size: 3-6cm thick and 15-20cm long