Marine algae - some aquarists cultivate it, some curse it. In the seventies and early eighties most aquarists considered healthy growths of micro or macroalgae an indicator of good water quality. In some ways that was correct. In other ways, those growths may have become an annoyance. In fact, there's no doubt that abundant growths of unwanted forms of algae have caused some aquarists to leave the hobby in disgust. Numerous books have dedicated portions of their text to marine algae. Nevertheless, I doubt whether the subject matter of causes and control has ever had the focus as appears in this booklet.