Aquarium Algae Control

Almost every algae problem comes down to one thing: an imbalance between light and nutrients. Scrubbing harder treats the symptom; balancing the tank treats the cause. This guide explains why algae appears, how to recognize the main types, and a practical plan to get your tank clear and keep it that way.

Why algae appears

Algae and plants compete for the same things: light and nutrients. When you give a tank more light (or a longer photoperiod) than the plants can use with the available CO2 and nutrients, the surplus feeds algae instead. New tanks are especially prone because plants have not established yet.

So the levers that cause algae are the same ones that cure it: photoperiod length, light intensity, CO2, and nutrient dosing — kept in balance.

The main types you'll meet

• Green spot and green film — on glass and slow leaves; usually too much light. Wipe and shorten the photoperiod.
• Hair and thread algae — fast green strands; often excess light or nutrients. Manually remove and rebalance.
• Black beard algae — dark tufts on edges and hardscape; usually unstable CO2 or too much light. The hardest to beat (see FAQ).
• Diatoms (brown dust) — common in new tanks; usually fades on its own as the tank matures.

A cleanup crew that actually helps

Animals won't fix an imbalance, but they keep surfaces grazed while you do:

• Nerite snails — the best all-round algae grazers, and they can't overpopulate freshwater.
• Amano shrimp — the hardest-working algae-eating shrimp; a planted-tank staple.

A key rule for any cleanup crew: never use copper-based products — copper is lethal to shrimp and snails.

The step-by-step fix

1. Shorten the photoperiod to 6–7 hours on a timer. This alone solves many outbreaks.
2. Check your light — too intense for a low-tech tank fuels algae. See our planted-tank light guide.
3. Dose fertilizer consistently so plants outcompete algae (in a planted tank).
4. Improve flow and CO2 stability if you run high-tech (helps against black beard algae).
5. Manually remove what you can, and add a cleanup crew.
6. Be patient — give the rebalanced tank two to three weeks.

Prevention beats cure

The lowest-algae tanks are well-planted, modestly lit on a consistent timer, lightly stocked, and not overfed. If you are setting up a planted tank, get the balance right from the start with our planted tank guide.

Treat algae as feedback, not bad luck. Correct the light-to-nutrient balance, let plants and a cleanup crew do their job, and a clear tank becomes the default rather than a constant battle.