How to Get Rid of White Algae in Fish Tanks

White algae in fish tanks can be a perplexing issue for aquarium enthusiasts. Contrary to popular belief, what is often referred to as “white algae” is not algae but rather a fungus. This comprehensive guide aims to provide a deep understanding of white algae, its causes, and the most effective methods for removal and prevention.

We’ll cover everything you need to know, from properly identifying white algae and its potential harms, to natural and chemical treatment options, utilizing helpful fish and inverts, comparison to similar issues like white mold, and frequently asked questions. With the information in this article, you’ll be equipped to banish white algae from your tank for good.

white algae in fish tank

Understanding White Algae

Aquarists often use white algae to describe the fuzzy white growths that can occur in aquariums, especially on new driftwood. However, this name is misleading – white algae is not a form of algae.

What is White Algae?

The white fungus-like growth typically referred to as “white algae” is more accurately described as a saprolegnia species. Saprolegnia is a genus of water molds that can infect fish and eggs, but also thrive on dead organic matter like driftwood and decaying plant material in aquarium environments.

Saprolegnia is not a plant or algae, but a filamentous saprophytic fungus. The long white threads of saprolegnia give it a cotton-like fuzzy appearance as it grows on submerged surfaces.

Appearance and Growth Patterns

  • Forms white cottony or wool-like clumps and patches
  • Thread-like filaments cluster together into tufts or nets
  • Attaches firmly to surfaces like driftwood, plants, decor
  • Rapid growth, can spread across tank quickly
  • More prolific in high organic environments

Saprolegnia thrives on dead and decaying matter. New driftwood is a prime target, releasing tannins and organic compounds as it soaks in the tank water. Saprolegnia uses these organics as an abundant food source.

The fast thread-like growth allows it to colonize driftwood, bogwood, and other biologically active decor quickly. As organic waste levels rise, saprolegnia may also appear on plant leaves, substrate, and other surfaces.

While not harmful, the lumpy white growths are unsightly and indicate issues like excess organics, poor cleanup crew, or stagnant water flow. Let’s look closer at the effects of saprolegnia to determine if treatment is needed.

Is White Algae Harmful?

Mostly, saprolegnia is not dangerous or detrimental in freshwater aquariums. However, some impacts are worth considering:

Dangers to Fish and Invertebrates

Saprolegnia is not toxic; dense patches may trap and suffocate small fish. Heavy growths can also promote low oxygen levels during decay.

Fish eggs and juvenile shrimp may be vulnerable to saprolegnia infection, which is relatively uncommon in home tanks.

Impacts on Aquatic Plants

Thick saprolegnia growth can smother plant leaves, blocking light and gas exchange. This is primarily an aesthetic concern.

Heavy buildup increases organic waste as the fungus decays, potentially fueling real algae blooms.

Overall, saprolegnia may indicate larger issues in tank maintenance and water quality. While not overtly dangerous, keeping growth under control enhances aesthetics and improves conditions for livestock.

Causes of White Algae

Understanding what allows saprolegnia fungi to thrive gives us clues to prevention and removal. Some key contributing factors include:

New Driftwood

Fresh driftwood releases tannins and dissolved organics that encourage saprolegnia, especially during the first few weeks in a tank. Boiling or soaking before use can reduce this effect.

Dead Algae Buildup

As plant or algae leaves decay, saprolegnia uses the debris as a food source and colonizes rapidly. Keeping tanks algae-free helps avoid this.

Low Oxygen Levels

Saprolegnia thrives in low O2 environments. Proper water circulation, surface agitation, and aeration prevent anoxic conditions suitable for growth.

Excess Light

High lighting combined with excess nutrients fuels saprolegnia growth. Reducing intensity or duration of light periods can help control growth.

High Organic Waste

Decomposing fish food, plant material, and other organics produce nutrients that feed saprolegnia. Efficient filtration and regular cleaning lessen organic accumulation.

Poor Water Circulation

Areas of low flow become oxygen depleted, allowing saprolegnia to thrive. Powerheads and directing filter outlets prevent stagnant zones.

High Phosphates and Silicates

Phosphates and silicates from tap water or gravel substrate can accelerate saprolegnia growth. Using RO/DI water and capping soil substrate reduces these compounds.

Now that we know what causes excess saprolegnia growth, we can move on to the most effective treatment methods.

Natural Remedies for White Algae

For moderate saprolegnia growth, natural and non-chemical remedies are ideal to protect livestock health. Here are some simple methods:

Manual Removal

Gently rubbing away saprolegnia tufts with a toothbrush, algae scraper, or cotton swab is safe and effective. Focus on decor, driftwood, and slow-growing plant leaves.

Reduce Lighting Periods

Excess light fuels growth. Cut back on intensity or duration to 6-8 hours daily until growth subsides.

Clean Filter Media

Clean mechanical media monthly to remove waste and organics before they break down in the filter.

Increase Water Circulation

Add a wavemaker, powerhead, air stone, or directional output to eliminate dead spots with low O2 and flow.

Introduce Fast-Growing Plants

Floating plants like hornwort rapidly uptake excess nutrients, outcompeting saprolegnia.

Use RO/DI Water for Water Changes

Using pure RO/DI water eliminates phosphates and silicates that feed growth.

Purigen Filter Media

Purigen absorbs dissolved organics before saprolegnia can utilize them. Recharge purigen regularly.

UV Sterilization

A UV sterilizer kills fungi spores and prevents them from taking hold in the aquarium.

With manual removal, reducing organics and nutrients, and improving tank conditions, saprolegnia can be controlled without chemicals.

Chemical Treatments for White Algae

Aquarists may consider chemical treatment options for severe cases of persistent saprolegnia growth. However, caution is required:

Hydrogen Peroxide

Low doses of hydrogen peroxide directly oxidizes saprolegnia hyphae. Use no more than 1 mL per gallon.

Excel or Glutaraldehyde

Glutaraldehyde-based liquid carbon supplements like Excel can be spot treated to control saprolegnia. Use sparingly and do not overdose.


Antibacterial meds containing erythromycin may inhibit saprolegnia growth. Make sure they are safe for invertebrates and plants.


Copper-based algaecides may damage saprolegnia at low doses. Copper can also harm invertebrates, so use with extreme care.

Potassium Permanganate

A diluted potassium permanganate dip kills spores on new plants and driftwood. Rinse thoroughly before adding to the tank.

Caution About Chemicals

Use any anti-fungal chemicals sparingly and only if natural methods fail. Remove invertebrates and scaleless fish before use. Overdosing chemical treatments can cause disastrous crashes.

Mild saprolegnia growth can often be managed through natural means like manual removal, reduced lighting, improved circulation, and regular tank maintenance. Use chemicals only as a last resort if the growth is rapidly worsening.

Fish and Inverts that Eat White Algae

While no fish or invertebrates directly consume saprolegnia, some can help clean up dead and detached pieces to prevent re-growth and filter clogging:

Plecos and Other Algae Eaters

Plecos, siamese algae eaters, otocinclus, and other clean up crews will nibble on saprolegnia debris. Their grazing limits accumulation.


Snails like nerites and mystery snails will eat dead matter containing saprolegnia, clearing space for new growth.


Shrimp pick at decaying pieces during their constant foraging. Amanos, cherry shrimp and vampire shrimp help clean substrata.

Otocinclus Catfish

Otos voraciously rasp algae from surfaces, incidentally removing saprolegnia in the process. A school helps accelerate cleanup.

While they do not eat live saprolegnia, these cleaners are useful for controlling accumulation of sheared fragments before they recolonize.

White Algae vs White Mold

White saprolegnia is often confused with a similar aquarium problem – white mold. While they look similar, there are some key differences:

Appearance and Growth Patterns

  • Saprolegnia has cottony filaments, mold is smooth
  • Mold forms circular patches, saprolegnia spread webs
  • Mold detaches easily, saprolegnia firmly attached
  • Mold grows on food waste, saprolegnia prefers wood

Dangers and Impacts

  • Saprolegnia low risk, mold releases toxins
  • Mold can kill livestock, saprolegnia generally harmless
  • Mold indicates sanitation issue, saprolegnia natural on new wood

Causes and Treatments

  • Mold caused by excess food and waste
  • Saprolegnia caused by wood organics and low O2
  • Remove moldy food manually and improve cleaning
  • Control saprolegnia with stable conditions and patience

While both appear white and fuzzy, mold is typically more dangerous and harder to remedy in aquariums. Identifying the differences allows proper treatment.

White Algae and Cloudy Water

Cloudy or milky water is sometimes misattributed to saprolegnia growth. However, white algae does not directly cause cloudiness. Separating the causes is important:

Causes of Cloudy Water

  • Bacterial blooms from excess waste organics
  • Green algae blooms from high nutrients
  • Suspended particles like sand or fine debris
  • Bacterial infections like mycobacteriosis

Clearing Cloudy Water

  • Improve filtration to remove particles and waste
  • UV sterilization kills floating bacteria and algae
  • Reduce feeding amounts and siphon debris
  • Treat bacterial infections with antibiotics

While saprolegnia indicates organic excess, it does not make the water cloudy itself. White water requires diagnosis and treatment of the specific cause for clarity.

White Algae on Aquarium Glass

In addition to wood and decor, saprolegnia may appear as fuzzy growths on the glass walls of the aquarium. Likely causes include:


  • Organic waste settling on glass
  • Low water circulation and dead spots
  • Overfeeding leading to excess nutrients

Manual Removal

  • Scrub glass gently with algae scrubber, pad, or cotton swab
  • Avoid abrasive scrubbers that can scratch acrylic
  • Clean just before a water change to remove debris

Scrubbing Accessories

  • MagFloat glass cleaners with removable scrub pad
  • SeaChem MagScraper for acrylic and glass
  • Cotton swabs for delicate cleaning of small areas

Chemical Cleaners

  • MagFloat Wonder Shells slowly dissolve to clean glass
  • PhosGuard in a media bag removes phosphates settling on glass
  • Spot treat tough areas with diluted Excel or hydrogen peroxide

Consistent glass cleaning, reduced feeding, and improved flow helps prevent recurrence once the glass is clear.

White Fungus on Aquarium Plants

Aquatic plants can also develop a white fungal coating resembling saprolegnia:


  • New plants still adapting to underwater life
  • Sensitive species like mosses and ferns
  • Tissue damage from rough handling or pests
  • Excess iron fertilization


  • Improve plant quarantine and acclimation procedures
  • Provide stable, consistent conditions for plant growth
  • Apply potassium permanganate dip to infected plants
  • Reduce iron dosing and perform more frequent water changes

The same cultivation techniques that promote healthy plant growth limits susceptibility to white fungus. Careful observation allows early treatment before it spreads.

Frequently Asked Questions

What causes white algae in fish tanks?

The saprolegnia fungus often called “white algae” is caused primarily by excess dissolved organics like tannins from new driftwood, decaying plant matter, and waste accumulation. Low oxygen and poor circulation also play a role.

How to get rid of white fungus on aquarium plants?

Improve plant care, manual removal, potassium permanganate dip, and addressing underlying issues like high iron levels or tissue damage can treat white fungus on plants.

What fish eat white algae?

No fish consume saprolegnia directly. But algae eaters like plecos and otocinclus help clean up dead debris before it spreads.

Is white algae harmful to fish?

Saprolegnia is generally harmless to fish. It can suffocate fish eggs if allowed to overgrow dense patches. But in most tanks it is just an aesthetic nuisance.

How can I prevent white algae from coming back?

The key is addressing the underlying causes. Maintain pristine conditions without excess waste or organics, use RO/DI water, improve circulation and oxygenation, and manually remove any new growth before it spreads.


White “algae” is a misnomer – the cottony growth is saprolegnia fungus. While usually not dangerous, keeping its growth in check improves tank aesthetics and cleanliness.

The keys are identifying and addressing the sources of excess organics, waste, and poor conditions that encourage saprolegnia. Natural methods like manual removal, stable water parameters, and tank maintenance are ideal for control in most cases.

With the deep understanding of identification, causes, treatments, and prevention covered in this guide, aquarists can successfully eliminate recurrent saprolegnia blooms and maintain clear and healthy aquarium environments.