My 100-gallon reef tank was recently overtaken by hair algae, an unfortunate plight that befalls many older reef tanks. I set up this tank in 1972 and cleaned it thoroughly only once, about 25 years ago. Putting off a long overdo cleaning, I decided to add an animal that was advertised as something that would eat this menacing algae. To this end I acquired what was sold as a “lettuce nudibranch” and placed it in the tank.