Top 5 Causes of Algae in Your Aquarium (And How to Prevent Them)

When you’re building a beautiful aquascape, nothing derails your hard work faster than an unexpected algae bloom. In the video below, we break down the five biggest causes of algae in freshwater tanks — based on real experience from a high‑tech aquascape that turned into a green swamp after a holiday break.

Whether you're a beginner or a seasoned aquascaper, understanding these causes will help you prevent algae before it takes over. 

1. Too Much Light

Excessive lighting — either too strong or too long — fuels algae growth. Many aquarists unknowingly run their lights at full intensity or leave them on for 10+ hours a day. Algae thrives on this.

Fix: Reduce intensity, shorten the photoperiod, and use a timer.

2. Excess Nutrients

Leftover food, fish waste, and over‑fertilising create nutrient imbalances. When plants can’t absorb everything, algae steps in.

Fix: Maintain consistent fertiliser dosing and avoid overfeeding.

3. CO₂ Instability

In high‑tech tanks, fluctuating CO₂ levels stress plants. Stressed plants can’t outcompete algae.

Fix: Ensure stable CO₂ injection and good surface agitation.

4. Poor Maintenance Routine

Skipping water changes or filter cleaning allows organics to build up — a perfect algae buffet.

Fix: Stick to a weekly maintenance schedule.

5. Imbalanced Hardscape or Planting

Sparse planting or too much exposed hardscape can leave nutrients unused, giving algae room to take over.

Fix: Increase plant mass and choose fast‑growing species.

Final Thoughts

Algae isn’t a sign of failure — it’s a sign of imbalance. By understanding these five causes, you can keep your aquascape healthy, vibrant, and algae‑free.