Nicotine doesn't just poison humans - it also poisons animals. It enters the aquarium through the air in the room and can cause massive damage there. Rigid ventral fins, erratic swimming and sinking are considered typical signs. Saltwater tanks are especially sensitive to nicotine. If aerators are operated to boot, the amount of nicotine entering the water increases considerably. Basically, the only thing that works is keeping the room smoke-free. However, the nicotine level in the water drops very quickly again – almost immediately after the smoker quits smoking. If you want to operate aerators, it is advisable to use a small prefilter with the activated carbon.