Controlling Turf and Hair Algae in a Reef Tank

Green turf and hair algae are the classic reef nuisance: fueled by excess nutrients and light. Learn the causes, why the new-tank ugly phase is normal, and how export plus herbivores restore balance.

Filamentous green hair algae and the low, carpet-like beds known as turf algae are the most common nuisance growths in reef and fish-only-with-live-rock systems. Algae are photosynthetic organisms, and turf assemblages form thick, sediment-trapping mats usually less than 15 cm tall that compete directly with corals for space and light. A little algae is normal; the problem is when it spreads unchecked across the rock.

What causes it

• Excess nutrients: elevated nitrate and phosphate, often from overfeeding or a heavy bioload, give algae the fuel to outgrow corals.
• Strong light plus nutrients: bright lighting combined with available nutrients accelerates growth.
• Low-flow dead spots: stagnant areas let detritus settle and feed algae.
• Immature systems: brand-new tanks pass through a natural algae-heavy stage before they balance out.

Nutrient export

The durable solution is to lower the nutrients that feed the algae. Protein skimming, a macroalgae refugium, granular ferric oxide for phosphate and regular water changes all pull nutrients out of the system. An algae turf scrubber turns the principle on its head, deliberately growing harvestable algae in a controlled spot; harvesting it removes nitrate and phosphate from the tank. Some keepers even use a fast-growing macroalga such as Caulerpa to out-compete nuisance turf for the same resources. See the reef nutrient management guide for target ranges.

Herbivores

A well-chosen clean-up crew grazes algae down while export catches up. Tangs and rabbitfish browse filamentous growth, and Halloween urchins (Tripneustes gratilla) are particularly effective at keeping turf and close-cropped hair algae in check. Emerald crabs and grazing snails add coverage. Herbivores manage the problem rather than cure it, so they work best alongside nutrient control rather than instead of it.

Flow, light and manual removal

Improve circulation to eliminate dead spots, review photoperiod and light intensity if growth is explosive, and scrub or manually remove heavy patches from the rock to give grazers and export a head start. Complete eradication is an unrealistic goal; steady management toward a balanced, lightly stocked system is what keeps turf and hair algae in check long term.