algae · both tank

GHA (Green Hair Algae)

GHA (Green Hair Algae) is filamentous green algae that grows in long strands on rock + glass. The most common nuisance algae in established marine tanks; signal of phosphate excess or nutrient imbalance.

Reviewed by Fast Aquatics husbandry team · Updated May 2026

Severity: Mild cosmetic - rarely lethal

Symptoms

Long stringy green strands attached to rock or glass
Tufts of bright green growth
Smothering corals on rockwork

What causes it

Excess phosphate (>0.05 ppm), excess light photoperiod, or nutrient imbalance from new live rock.

Treatment options

Always treat in a separate quarantine tank.

Manual removal + flow. Pull out by hand during water changes; toothbrush smaller patches. Increase flow to discourage regrowth.

Reduce phosphate. Run GFO in a reactor; target PO4 <0.05 ppm. Most effective long-term solution.

Algae-eating CUC. Add turbo snails, emerald crabs, lawnmower blenny, or kole tang. They eat GHA but won't outpace a fed bloom alone.

Reduce photoperiod. Cut lighting from 10 hours to 6-8 hours during the bloom; restore once cleared.

Prevention

Maintain low phosphate, balanced photoperiod, strong CUC, regular water changes.

Frequently asked questions

What does GHA (Green Hair Algae) look like?

Long stringy green strands attached to rock or glass. Tufts of bright green growth. Smothering corals on rockwork.

What causes GHA (Green Hair Algae)?

Excess phosphate (>0.05 ppm), excess light photoperiod, or nutrient imbalance from new live rock.

How is GHA (Green Hair Algae) treated?

Manual removal + flow: Pull out by hand during water changes; toothbrush smaller patches. Increase flow to discourage regrowth.

Can GHA (Green Hair Algae) be prevented?

Maintain low phosphate, balanced photoperiod, strong CUC, regular water changes.

How fatal is GHA (Green Hair Algae)?

Mild cosmetic - rarely lethal

Browse the full disease database for 45 aquarium conditions with treatment protocols, or check the care library for prevention-focused husbandry guides. Use our symptom matcher to rank likely diseases from observed signs, the water parameter checker to diagnose related water-quality issues, or the QT timeline calculator to plan a treatment schedule.