Troubleshoot
Hair Algae in a Planted Tank: Causes + Fix Order
Hair algae is long green filaments that wave in the current or wrap around stems—not dark brush tufts (BBA) and not stiff staghorn branches. Fix light hours and plant uptake before you spot-treat forever.
- Hair / thread
- Green filaments
- Light vs uptake
- Fix order
What you’re seeing
Confirm hair algae: soft green threads you can pinch and pull, often on fast stems, filter outlets, and open hardscape. A wipe test on glass does nothing—this is not dust film.
| Pattern | Likely driver |
|---|---|
| Long green strings waving in flow | Light hours ahead of plant mass |
| Hair after a big trim / melt week | Nutrients leftover + open space |
| Hair only in one bright corner | Local PAR hotspot |
| Dark wiry tufts on wood instead | That’s BBA—different playbook |
See also the algae ID chart if you are mixing names.
Likely causes (ranked)
Photoperiod / PAR ahead of uptake
Sparse tanks under 8–10h LEDs grow hair faster than stems.
Quick test: Lights >7–8h; few fast plants; hair on the brightest side.
Nutrient leftover after melt or overfeed
Ammonia/organics plus open light = filament bloom.
Quick test: Recent trim, melting Crypts, leftover food.
Unstable CO₂ with high light
Plants stall daily; algae uses the gap.
Quick test: Drop checker swings; pearling uneven.
Low flow pockets around stems
Hair colonizes still water around plant clumps.
Quick test: No leaf sway in the hair zone.
Fix order
-
Step 1
Shorten light 10–14 days
Drop to ~6–7 hours or raise the fixture. Don’t add more intensity hoping plants “outrun” hair overnight.
-
Step 2
Manual removal
Twirl filaments on a toothbrush or chopsticks; siphon loose strands. Trim wrapped leaves.
-
Step 3
Stabilize carbon + planting
Steady CO₂ if you inject—see the CO₂ hub. Add cheap stem mass (hygrophila, wisteria) to soak leftovers.
-
Step 4
Spot-treat leftovers only
Liquid carbon or dilute peroxide on isolated clumps—filter off briefly, livestock safe. Never bleach the whole tank.
When to escalate
- Stiff branching tufts on hardscape → staghorn algae.
- Slimy blue-green sheets on sand → cyanobacteria.
- Pea-soup water → green water.
- Parent hub → algae control field guide.
Helpful products
Related guides
- Algae ID chart — Don’t mix names
- BBA fix order — Dark tufts
- CO₂ hub — Stability
- All calculators — Tools
FAQ
Is hair algae the same as black beard?
No. Hair is green filaments; BBA is dark brushy tufts on edges and wood.
Will Amano shrimp clear it?
They help loose strands, not a tank full of hair. Fix light first.
Should I blackout for a week?
A 2–3 day blackout can slow hair, but 6–7h lights + removal usually beats a long blackout.
Does more fertilizer stop hair algae?
Only if plants were starved and you also cut light. Dumping macros into a bright empty tank often worsens it.
How long until it recedes?
New growth stays clean in 1–3 weeks if hours and uptake are fixed; old strands need pulling.
Can I use copper algaecide?
Avoid with shrimp/snails. Prefer mechanical + photoperiod.
Aqua Plants Hub Editorial
