Algae eaters

The true Siamese algae eater, Crossocheilus oblongus, is the one fish that reliably eats black beard algae, and it does it best while young and hungry. It grows to 6 inches (16 cm), shoals, and lists a 37 gallon (140 liter) tank. The flying fox and silver flying fox are sold under the same name and eat far less of it. Amano shrimp pick at black beard algae too, and a squad of them keeps new growth down once the fish has done the heavy work.

Nerite snails are the answer for glass, and the zebra, tiger and horned nerites rasp even the hard green spot algae that nothing else touches. A bristlenose pleco does the same on wood and rock and stays at 5 inches (12.5 cm), unlike the common pleco. In a cool tank with strong flow the hillstream loaches graze the glass and stones the way they graze a river.

The American flagfish eats hair algae the way a goat eats grass, and it is the only fish here that does. It wants cooler water, 63 to 73°F (17 to 23°C), and a 20 gallon (70 liter) tank. Amano shrimp and cherry shrimp pull threads apart and eat them, and a large enough group makes a visible difference in a week.

In a nano tank the horned nerite, at 5 gallons (19 liters), and a few Amano or cherry shrimp do the work without adding a fish. In a planted tank the same shrimp plus a group of otocinclus clean leaves without damaging them, which no pleco can promise. Skip plecos in anything under 20 gallons.

Fish need groups and a mature tank, shrimp need a tank with no copper in the medications and no fish that eat them, and snails need calcium in the water or their shells pit. Whichever you choose, it is treating a symptom. Algae grows on light, nutrients and time, so shorten the light to six or eight hours, feed less, change more water, and plant fast growers to take the nutrients first. The eater keeps things tidy between those chores.