The short answer
Hair algae — long, soft green strands that cling to plants and hardscape — is a sign that light and nutrients are out of balance, usually too much of both. To beat it: remove as much as you can by hand, cut your photoperiod to 6–8 hours on a timer, and grow more plants so they out-compete the algae for the same nutrients. There’s no single spray that fixes it — you’re rebalancing the tank, not just cleaning it.
Remove it manually first
Physical removal is the fastest way to knock hair algae back. Twirl the strands around an old toothbrush or a chopstick — they wind up like candy floss and lift off in clumps. Pull it off plant leaves gently so you don’t tear them, and syphon out loose bits during your next water change. Getting rid of the bulk means less algae releasing spores and less for you to fight next week.
Fix the cause: light and nutrients
Hair algae feeds on the same light and nutrients your plants use, so it thrives whenever there’s a surplus of either.
- Trim the light. Put your aquarium light on a timer and keep it to 6–8 hours a day. Long or overly bright lighting is the number-one trigger. See our planted-tank light picks.
- Feed less, stock sensibly. Overfeeding and overstocking dump extra nitrate and phosphate into the water — algae fuel. Feed only what fish clear in a couple of minutes.
- Grow more plants. Fast growers (stem plants, floaters) soak up nutrients before algae can. A well-planted tank with balanced fertilisers and stable CO2 rarely has a hair-algae problem.
Keep it from coming back
Consistency wins. Do a weekly 25–30% water change to export excess nutrients, keep that photoperiod on a timer, and stay on top of any early strands before they spread. If you want a broader plan, read our full guide on how to get rid of aquarium algae, and see why you have so much algae for the root causes.