How to get rid of algae in a planted tank

Algae isn't an invader you fight — it's a symptom. It blooms when the balance between light, CO₂ and nutrients tips in its favour. Scrubbing and dosing algaecides only buys time; the lasting fix is correcting the imbalance so healthy plants outcompete it.

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The core principle

Plants and algae compete for the same light and nutrients. When plants are thriving, they soak up resources and release compounds that suppress algae. When plants struggle — too much light for the available CO₂, or a nutrient gap — the leftover energy and nutrients feed algae instead. So the real question is never "how do I kill algae" but "why are my plants not winning?"

Identify the type — it points to the cause

Algae	Looks like	Usual cause
Green spot (GSA)	Hard green dots on glass/old leaves	Low phosphate, strong light
Green dust (GDA)	Fine green film on glass	New-tank instability; matures out
Black beard / brush (BBA)	Dark tufts on edges & hardscape	Low or fluctuating CO₂, poor flow
Diatoms	Brown dusty coating	New tank, settles on its own
Hair / thread	Long green strands	Excess light/nutrients vs CO₂
Cyanobacteria	Slimy blue-green sheets	Low flow, organic build-up

Fix the root cause

• Reduce light first. Shorten the photoperiod to 6–7 hours and lower intensity. Light is the accelerator for both plants and algae — most outbreaks ease when you dial it back.
• Stabilise CO₂ / carbon. If you inject, keep it steady and well-distributed; fluctuating CO₂ is the classic trigger for black beard algae.
• Balance nutrients. Don't starve the tank to "starve algae" — that backfires by weakening plants. Keep macros and micros consistent so plants stay healthy.
• Improve flow & clean up. Good circulation and removing decaying leaves/mulm starve cyanobacteria and BBA.
• Stay consistent on water changes and add a clean-up crew (otocinclus, amano shrimp, nerite snails) for grazing.

Manually remove what you can, then give the corrected balance two to three weeks to take hold. Patience beats panic dosing.

Why a log is your best algae tool

Outbreaks always trail a change — a longer photoperiod, a missed water change, a CO₂ that drifted, a nitrate that climbed. When your light hours, dosing, tests and maintenance are all dated in one place, you can scroll back to the week before the algae started and usually spot the exact trigger.

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