Azolla Aquarium: The Complete Guide to Growing and Caring for Floating Ferns -

Aquatic plants are an essential part of aquariums, not only for their beauty but also for the ecological balance they bring to the water system. While many hobbyists are familiar with floating plants like Duckweed, Salvinia, and Frogbit, there’s another remarkable option that’s gaining popularity—Azolla, a floating fern known for its rapid growth, nitrogen-fixing ability, and lush green (sometimes reddish) appearance.

In this comprehensive guide, we will dive deep into everything you need to know about Azolla aquariums—from its biology, benefits, and growing requirements to potential challenges, maintenance, and frequently asked questions.

Table of Contents

What is Azolla?

Azolla, often referred to as mosquito fern or water fern, is a genus of small floating ferns that belong to the family Salviniaceae. Unlike most aquatic plants, Azolla is unique because of its symbiotic relationship with cyanobacteria (Anabaena azollae), which allows it to fix atmospheric nitrogen directly into the water.

This makes Azolla not just a plant, but also a natural fertilizer and nutrient regulator, making it highly valuable in aquariums and even in agriculture.

Key Characteristics:

Floating Fern – Azolla floats freely on the water surface without rooting.
Rapid Growth – Under favorable conditions, it can double its biomass within 3–5 days.
Color Changing Ability – Usually green, but turns reddish under bright light or nutrient stress.
Nitrogen-Fixing Ability – Provides a natural source of nitrogen, enriching the aquarium ecosystem.

Types of Azolla for Aquariums

There are several species of Azolla, but only a few are commonly kept in aquariums.

1. Azolla filiculoides (Red Azolla)

Turns a reddish hue under bright light.
Popular in aquariums for its striking appearance.

2. Azolla pinnata

Delicate feathery leaves.
Commonly used in rice paddies but can be adapted for aquariums.

3. Azolla caroliniana

Widespread in North America.
Small, dense growth, making it suitable for nano aquariums.

4. Azolla microphylla

Very small and compact leaves.
Easy to control in aquariums due to its slower spread compared to other species.

Why Keep Azolla in Aquariums?

Adding Azolla to an aquarium is more than just an aesthetic choice—it provides functional and ecological benefits.

1. Natural Algae Control

By covering the water surface, Azolla blocks excess light, thereby reducing algae growth.

2. Nutrient Absorption

Azolla absorbs nitrates, phosphates, and ammonia, keeping water conditions stable.

3. Oxygen and Nitrogen Balance

Through photosynthesis, it produces oxygen, while its nitrogen-fixing ability enriches the water.

4. Shade and Shelter

Provides shaded areas for fish that prefer subdued lighting.
Protects fry and shrimp from predators.

5. Aesthetic Beauty

Its green and red shades give the aquarium a natural and vibrant look.

6. Eco-Friendly Filtration

Acts as a natural filter, reducing the workload of mechanical and chemical filtration systems.

Ideal Tank Conditions for Azolla

Azolla is hardy and adaptable, but it thrives best under certain conditions.

1. Lighting

Moderate to bright lighting is ideal.
Under strong light, Azolla often turns reddish, enhancing its beauty.

2. Water Parameters

Temperature: 18–28°C (64–82°F).
pH: 6.0–7.5 (slightly acidic to neutral).
Hardness: Soft to moderately hard water.

3. Water Flow

Prefers still or slow-moving water.
Strong currents may submerge or damage delicate fronds.

4. Tank Size

Suitable for all tanks, from small nano setups to large aquascapes.
Works well in outdoor ponds too.

How to Grow and Propagate Azolla in Aquariums

Growing Azolla is remarkably easy, making it suitable for beginners.

Planting Method

Simply place Azolla on the water surface. It will float naturally.
Ensure there’s enough light and nutrients for healthy growth.

Propagation

Vegetative reproduction is the primary method.
Small fragments of Azolla can grow into new plants, allowing it to spread quickly.

Growth Tips

Trim regularly to prevent complete surface cover.
Supplement with liquid fertilizers if the tank lacks nutrients.
Provide a balanced photoperiod of 8–10 hours of light daily.

Azolla in Different Aquarium Types

Azolla adapts well to various aquarium setups:

1. Community Aquariums

Provides shade, reducing fish stress.
Absorbs excess nutrients from fish waste.

2. Betta Tanks

Bettas love resting under floating plants like Azolla.
Mimics their natural habitat with shaded spots.

3. Shrimp Tanks

Creates biofilm on roots and fronds, which shrimp love to graze on.
Provides shelter for baby shrimp.

4. Breeding Tanks

Excellent hiding places for fry.
Reduces predation risks.

5. Planted Aquascapes

Complements rooted plants.
Offers surface cover, reducing algae outbreaks.

Common Problems with Azolla in Aquariums

While Azolla is easy to maintain, a few issues may arise:

1. Overgrowth

Can cover the entire surface rapidly.
Solution: Regular thinning and manual removal.

2. Nutrient Deficiency

Leaves may turn pale or yellow.
Solution: Add liquid fertilizers or ensure sufficient nutrients.

3. Melting or Sinking

Caused by strong water currents or poor conditions.
Solution: Maintain stable parameters and low flow.

4. Blocked Gas Exchange

Excessive surface cover prevents oxygen exchange.
Solution: Always leave some surface area clear.

How to Control Azolla Growth

Since Azolla grows fast, managing it is essential.

Regular Harvesting – Remove excess weekly.
Light Management – Reduce light intensity to slow down growth.
Surface Agitation – Gentle water movement prevents mat formation.
Tank Companions – Herbivorous fish may nibble on Azolla, helping to control it.

Step-by-Step Guide: Adding Azolla to Your Aquarium

Quarantine New Plants – Rinse and isolate before adding to the main tank.
Place on Surface – Gently float them on the water.
Adjust Lighting – Provide moderate lighting for best results.
Monitor Spread – Observe how quickly it grows.
Thin Regularly – Keep balance between Azolla, light, and gas exchange.

Advantages of Azolla Over Other Floating Plants

Compared to other floating plants, Azolla has unique benefits:

Easier to manage than Duckweed, which can be invasive.
More nitrogen-fixing ability than Salvinia.
Smaller and more compact than Frogbit or Water Lettuce.
Adds unique red coloration that many floating plants lack.

Practical Uses of Azolla Beyond Aquariums

Azolla isn’t just an aquarium plant—it has other ecological and agricultural uses:

Natural Fertilizer – Widely used in rice paddies for nitrogen fixation.
Animal Feed – Rich in protein, used as livestock and fish food.
Pest Control – Covers water surfaces in ponds, reducing mosquito breeding.
Water Purification – Helps remove heavy metals and toxins.

Final Thoughts

Creating an Azolla aquarium is an excellent choice for aquarists who want a unique, eco-friendly, and functional floating plant. Its rapid growth, nitrogen-fixing ability, and striking colors make it one of the most versatile plants available.

By maintaining proper lighting, trimming regularly, and ensuring balanced water conditions, Azolla can thrive without overwhelming your tank. Whether you’re keeping fish, shrimp, or bettas, Azolla offers countless benefits—from algae control to providing shelter.

For aquarists looking for a low-maintenance but high-impact plant, Azolla is a perfect choice.

FAQs About Azolla Aquarium

1. Is Azolla safe for aquariums?

Yes, Azolla is completely safe and even beneficial for aquariums. It helps with nutrient absorption and provides shelter for fish and shrimp.

2. Does Azolla produce oxygen?

Yes, Azolla produces oxygen through photosynthesis, but excessive growth may block oxygen exchange at the surface.

3. How fast does Azolla grow?

Under good conditions, Azolla can double its coverage in 3–5 days, so trimming is essential.

4. Can Azolla survive in low light?

It can survive in low light but will grow slowly and may turn pale. Bright light gives it a reddish color.

5. Do fish eat Azolla?

Some herbivorous fish and goldfish may nibble on Azolla, but most aquarium species don’t eat it.

6. Is Azolla better than Duckweed?

Yes, many aquarists prefer Azolla because it’s easier to control, has more aesthetic value, and fixes nitrogen naturally.

7. Can Azolla grow with a strong filter?

Strong water flow may damage or sink Azolla. It grows best in tanks with gentle surface movement.

8. How do I stop Azolla from taking over my tank?

Regularly harvest excess plants and leave some open water for gas exchange.