Common Mistakes with Diatoms in New Tanks and How to Avoid Them

One of the most frustrating experiences for new aquascapers is seeing an unsightly brown film crawling over rocks, glass, and plants within just weeks of setting up a new tank. If you’re noticing this, you’re likely dealing with diatoms—an all-too-common occurrence in new aquariums. While diatoms are harmless, their appearance can be discouraging for beginners and experts alike. Thankfully, with some basic knowledge, you can avoid or quickly overcome a diatom outbreak in your new aquascape.

What Are Diatoms and Why Do They Appear in New Tanks?

Diatoms are a type of algae, specifically a group of microscopic algae known for their brown, dusty appearance. They thrive in environments with excess silica, a nutrient commonly found in new aquariums, especially those set up using new substrates, untreated tap water, and uncycled filters. Diatom outbreaks are most common during the first few weeks of an aquarium’s life cycle when beneficial bacteria have yet to establish themselves fully.

Key Triggers for Diatom Blooms

• High levels of silicates (silica) in water
• Using new substrates that slowly leach silicates
• Insufficient beneficial bacteria due to an immature nitrogen cycle
• High levels of phosphate or fluctuating water parameters
• Inadequate lighting cycles or weak filtration

Common Mistakes Aquascapers Make with Diatoms

Mistake #1: Overreacting and Scrubbing Excessively

It’s tempting to scrub every surface clean at the first sight of brown algae. However, excessive scrubbing can disrupt beneficial biofilms and stress livestock.

How to Avoid:

• Gently wipe away diatoms during routine maintenance rather than deep-cleaning every surface.
• Allow your aquarium to mature naturally and focus on maintaining stable water parameters.

Mistake #2: Ignoring Water Source Quality

Tap water often contains high levels of silicates and phosphates, which fuel diatom growth. Many aquascaping beginners overlook this crucial factor.

How to Avoid:

• Consider using RO/DI (reverse osmosis/deionized) water instead of untreated tap water.
• Test your water source regularly for silicates and phosphates using aquarium test kits.

Mistake #3: Overfeeding and Excess Nutrients

Overfeeding fish or shrimp increases leftover food and waste, leading to elevated phosphate levels—another factor that promotes diatom growth.

How to Avoid:

• Feed livestock small amounts they can consume in a few minutes.
• Remove uneaten food and perform regular water changes.

Mistake #4: Insufficient Biological Filtration

An uncycled or immature filter allows nutrients like ammonia and nitrite to accumulate, creating favorable conditions for diatoms and other unwanted algae.

How to Avoid:

• Always cycle your aquarium fully before adding delicate plants or livestock.
• Add beneficial bacteria supplements to speed up the cycling process.

Mistake #5: Lack of a Cleanup Crew

Certain inhabitants—like Otocinclus catfish, nerite snails, and Amano shrimp—are natural diatom grazers. Not including them in your new aquascape can slow down the removal process.

How to Avoid:

• Introduce a suitable cleanup crew once your tank is cycled and stable.
• Research compatibility before adding algae-eating species to your aquascape.

Expert Tips to Prevent and Control Diatoms

• Patience is key: Diatom blooms usually disappear naturally after several weeks as your tank matures.
• Optimize lighting: Provide an appropriate light schedule (6-8 hours/day) to avoid encouraging unnecessary algae growth, but remember diatoms are less dependent on strong light compared to green algae.
• Regular maintenance: Perform partial water changes (20-30% weekly) to dilute excess nutrients and silicates.
• Monitor parameters: Keep an eye on ammonia, nitrite, nitrate, phosphate, and silicate levels with reliable test kits.
• Use quality substrate and rocks: Choose aquascaping materials low in silicates to limit the chance of outbreaks.

When Should You Worry About Diatoms?

In most cases, diatoms are harmless and a normal part of the aquarium maturation process. However, persistent, heavy blooms lasting beyond two months, or blooms occurring in established tanks, may indicate an underlying problem. In these cases, test your water, review your filtration system, and consider reviewing our beginner’s algae guide for further troubleshooting tips.

Conclusion: Achieve a Clean, Diatom-Free Aquascape

Diatoms are a rite of passage for many new aquascaping setups, but they need not spoil your enjoyment—or the beauty—of your carefully crafted aquarium. By understanding the common mistakes and taking proactive steps, you’ll be well on your way to a pristine, healthy aquascape. Remember: patience, balanced nutrients, and good maintenance routines are your best tools.

Ready to upgrade your aquascaping skills? Explore our in-depth guides and join our community at Aquascaping Academy for expert tips, step-by-step tutorials, and support. Have a question or want to share your experience? Contact us or comment below!