If you’ve recently set up a new aquarium and are noticing a brownish film coating your plants, rocks, and substrate, you’re not alone. Diatoms—commonly known as brown algae—are a rite of passage for many in the aquascaping hobby. While unsightly, these early invaders are usually harmless and temporary. This comprehensive playbook will help you identify, troubleshoot, and ultimately defeat diatoms, setting your planted tank up for long-term success.

What Are Diatoms? Understanding Brown Algae in Aquascaping

Diatoms are a type of single-celled algae characterized by their silica-based cell walls and unmistakable brown or rust-colored appearance. They thrive in environments with high silicate and nutrient levels—common in new aquarium setups. For aquascaping enthusiasts, knowing how to recognize diatoms is the first step toward a balanced, healthy aquarium.

Why Do Diatoms Appear in New Tanks?

Diatom outbreaks typically occur during the cycling phase of a new aquarium. Here’s why:

• High Silicate Content: New tanks often feature substrates or water sources rich in silicates, which diatoms love.
• Uncycled Filter: Immature biological filtration means higher levels of organic nutrients.
• Low Plant Competition: Young aquatic plants are often not yet established enough to outcompete algae for nutrients.
• Inconsistent Lighting: Excessive light, or improper duration, can give algae a head start during the tank’s “new” phase.

How to Identify Diatoms in Your Aquascape

Is it really diatoms, or another type of algae? Look for these hallmarks:

• Brown, dusty coating on glass, substrate, rocks, and plant leaves
• Easy to wipe off with a finger or sponge
• Appears rapidly in the first few weeks after setup
• Does not string or mat together (unlike green or hair algae)

Step-By-Step Diatom Troubleshooting Guide

1. Manual Removal

Start by gently wiping down affected surfaces with a soft sponge or aquarium-safe cloth. Perform regular water changes (25-50% weekly) to export excess silicates and nutrients.

2. Optimize Your Filtration

Ensure your filter is operating efficiently and is sized appropriately for your tank. Consider adding filter media that absorbs silicates (such as Seachem PhosGuard or Purigen) to further reduce diatom fuel.

3. Check Your Water Source

Tap water often contains silicates. If feasible, switch to reverse osmosis (RO) water for aquarium top-offs and water changes to drastically reduce silicate levels in your aquascape.

4. Establish a Robust Plant Mass

Healthy, fast-growing aquatic plants outcompete algae for nutrients. Plant heavily from the start, using easy, hardy species for cycling new aquariums. For more plant selection tips, visit our beginner aquascape plants guide.

5. Control Lighting

Limit lighting to 6-7 hours per day during the initial cycling period. Too much light will fuel algae faster than plants can absorb nutrients.

6. Introduce Algae Eaters

Once your tank is cycled and parameters are stable, add a cleanup crew. Nerite snails, Otocinclus catfish, and Amano shrimp are excellent for mowing down diatoms without harming delicate aquascaping plants.

7. Practice Patience!

Most importantly, remember that diatoms are a normal phase in new tank maturation. With proper care, they often disappear on their own within 2-8 weeks as your aquatic ecosystem stabilizes.

Preventing Future Diatom Outbreaks

• Stick to regular water changes and glass cleaning
• Maintain a healthy, densely planted aquascape
• Monitor water parameters (especially silica and phosphate)
• Avoid overfeeding livestock
• Adjust light duration as needed to match plant growth

When to Worry: Diatoms vs. Persistent Algae Issues

If brown algae lingers for more than 8-10 weeks, or rapidly reappears after each cleaning, test your source water for silicates and review your maintenance routine. Persistent outbreaks may indicate an underlying imbalance or water quality issue.

If you’re dealing with green hair algae or blue-green algae, check out our troubleshooting guides on green hair algae control and cyanobacteria management.

Conclusion

Diatoms are almost a badge of honor for new aquascapers. They may be unsightly, but with a little patience and the practical steps in this playbook, your new tank will soon be sparkling clean—and your plants thriving. For many, the right approach is a blend of good husbandry, balanced nutrition, and time.

Have questions or want to share your experience troubleshooting diatoms in your aquarium? Join the conversation in the comments below or explore more expert aquascaping advice on our blog!