They remove unwanted organics as well as ink and heavy metals. Cuttlefish will ink if stressed. The ink should be siphoned out of the aquarium, and the cause of the stress should be located and removed if possible. Lighting Cuttlefish don't need any special kind of lighting. Keeping the lights to a minimum also reduces the growth of algae and one or two standard flourescent bulbs will suffice.
New cuttlefish are especially prone to inking if their environment rapidly changes.
For example, if someone bumps the tank or the lights come on suddenly they may ink. In addition to inking, nervous cuttlefish may react by jetting and hitting the side of the aquarium. This can cause the delicate skin to rip, exposing the muscle below, and is termed 'butt burn' by Dr. Jean Boul. This lesion can get worse if the animal continues to jet into the side of the tank and it can become infected. If you see this happening turn on the lights slowly and try not to startle your cuttlefish.