Hair algae might make your tank look like a green mess, but don’t panic. This is one of the easiest pests to deal with in the reefing world. Whether it’s a small patch or a full-on takeover, green hair algae (GHA) is completely manageable with the right strategy. If your tank looks like a chia pet gone rogue, here’s how to take back control and keep your reef looking its best.

What Is Hair Algae?

Green hair algae (GHA) is a common filamentous algae that grows in strands or tufts across rocks, sand, equipment, and even coral skeletons. It gets its name from its soft, wavy appearance that resembles fine green hair. Most of the time, you’re dealing with species like Derbesia, but let's not over complicate it. If it’s green and stringy, it’s probably GHA.

Just be careful not to confuse it with bryopsis. This similar-looking pest can be harder to remove. Bryopsis is stiffer, more feather-like in appearance, and more stubbornly anchored. If that sounds more like your issue, Help! I Wrecked My Tank Episode 2: How to Handle Bryopsis Algae is for you. 

Green Hair Algae vs. Bryopsis

Where Does It Come From?

Unfortunately, you probably introduced it without knowing through live rock, live sand, coral frags, or even new snails. The spores can be nearly invisible and hitchhike their way into your tank. But don’t beat yourself up. It happens to the best of us.

Here are a few smart ways to reduce the risk:

  • Keep the lights off during the cycle if you’re starting a new tank with live rock or sand.
  • Remove corals from frag plugs or brush the plugs before adding them if they can't be removed.
  • Scrub snail and hermit crab shells.
  • Add herbivorous fish and inverts early to keep things balanced.

How to Get Rid of Hair Algae

Getting rid of hair algae is all about a three-pronged approach: natural predators, physical removal, and nutrient control.

1) Natural Predators

A solid cleanup crew is your first line of defense. Green hair algae is soft and palatable, so many reef-safe herbivores will go to town on it.

Fish Invertebrates
  • Tangs (especially Zebrasoma species)
  • Rabbitfish
  • Blennies (like lawnmower or starry)
  • Mexican Turbo Snails
  • Black Banded Trochus
  • Astraea Snails
  • Money Cowries
  • Tropical Abalone
  • Tuxedo or Pincushion Urchins

If you’re just starting a tank, live copepods like AlgaeBarn EcoPods can help control algae before it becomes visible by consuming its early stages.

Copepods

2) Pysical Removal

If it’s long and wispy, your cleanup crew might not be enough. That’s when it’s your turn to pitch in.

The best method is the pinch and siphon technique:

  • Use your thumb and a siphon hose to pinch off clumps of algae and immediately suck them out.
    • Extra Tip: Smaller diameter tubing like 1/4" RO tubing can help you get into tight spaces.
  • Do not scrub it off with a brush. This just spreads fragments around and makes things worse.

3) Nutrient Control

In addition to lighting, algae growth is fueled by nutrients like phosphate and nitrate, so keeping these levels in check is essential. Keep in mind that if your tank is already overrun with algae, phosphate and nitrate may appear undetectable on tests because the algae is rapidly consuming them. Even if levels seem low, it’s still important to regularly monitor both nutrients to stay ahead of potential issues.

Ideal nutrient levels:

  • Phosphate: 0.02 to 0.06 ppm
  • Nitrate: 5 to 10 ppm

What if your phosphate and/or nitrate levels are too high?

  • Perform water changes (it may also be a good idea to test your source water for contamination)
  • Improve filtration (like refugiums, algae scrubbers, or macroalgae reactors)
  • Consider mechanical filtration like fleece rollers to remove waste before it breaks down

From Overrun to Under Control

Green hair algae can feel overwhelming, but it’s beatable! Once you knock it back, it usually stays under control with good habits. A great cleanup crew, some physical effort, and stable nutrients go a long way. Stay consistent, and you’ll be back to enjoying your reef in no time.

Just remember, hair algae won’t be the last challenge your reef throws at you. Be sure to check out the rest of the “Help! I Wrecked My Tank” series for tips on battling other reef tank pests.