Biofloc Technology: A Practical Introduction to Biofloc Aquaculture

Introduction

Aquaculture produces something every farmer has to manage: waste.

Feed, feces, uneaten feed and metabolic waste continuously introduce organic matter and nitrogen into the culture environment. In conventional aquaculture systems, a significant part of this waste may be managed through water exchange, filtration, sediment removal or other treatment methods.

Biofloc Technology (BFT) takes a different approach.

Instead of treating nutrients only as waste that needs to leave the system, Biofloc aims to transform, retain and recycle nutrients within the culture environment through biological processes.

Microorganisms use organic matter and nutrients as substrates for growth. Under suitable conditions, microbial biomass develops and forms aggregates known as bioflocs.

These aggregates can become an important part of the culture ecosystem.

But Biofloc is much more than cloudy or brown water.

A successful Biofloc system is a managed microbial ecosystem in which:

Animals + Microorganisms + Carbon + Nitrogen + Oxygen + Solids + Water Chemistry

continuously interact.

Understanding these relationships is the foundation of successful Biofloc aquaculture.

1. What Is Biofloc Technology?

Biofloc Technology is an aquaculture management approach that promotes the development of microbial communities within the culture system.

The fundamental concept can be simplified as:

Feed → Waste → Microorganisms → Biofloc → Nutrient recycling

When feed enters the system, only part of its nutrients become animal biomass.

The remainder eventually enters the culture environment through:

• feces
• metabolic waste
• dissolved organic compounds
• uneaten feed
• nitrogenous compounds
• other organic material

In a Biofloc system, microorganisms can transform and assimilate a portion of these compounds.

Heterotrophic microorganisms can use available organic carbon and incorporate inorganic nitrogen into microbial biomass. At the same time, other microbial processes, including nitrification, can transform nitrogen compounds through different biological pathways.

The microbial biomass and associated particles can aggregate into bioflocs.

A biofloc may contain combinations of:

• bacteria
• algae
• protozoa
• fungi
• organic particles
• inorganic particles
• detritus
• extracellular polymeric substances

The exact composition varies between systems.

Therefore, Biofloc should not be understood as a single organism or a single biological process.

Biofloc Technology is the management of a complex microbial ecosystem within an aquaculture system.

2. Biofloc vs. Biofloc Technology

The terms biofloc and Biofloc Technology are often used as though they mean the same thing. They are related, but there is an important distinction.

Biofloc

Biofloc refers primarily to the microbial aggregates and associated particles that develop within the culture water.

Biofloc Technology

Biofloc Technology refers to the aquaculture approach used to establish and manage the conditions that allow these microbial communities and aggregates to develop. This distinction matters because simply having visible floc does not mean a system is functioning correctly.

A farmer should not aim to produce:

"As much floc as possible."

The objective is to maintain:

A stable and functional microbial community capable of processing the biological load placed upon the system.

3. The Basic Biofloc Cycle

The Biofloc concept can be visualized as a continuous nutrient cycle.

Step 1 — Feed enters the system

Feed is provided to the cultured animals. It contains nutrients including protein, carbohydrates, lipids, minerals, nitrogen and organic carbon.

Step 2 — Animals consume the feed

The animals consume the feed and convert a portion of its nutrients into animal biomass.

Step 3 — Waste and nutrients enter the water

Not all nutrients are retained by the animals. Metabolism, feces and uneaten feed introduce organic matter and nitrogen into the culture environment.

Step 4 — Microorganisms process the nutrients

Microbial communities use organic compounds and inorganic nutrients as substrates for growth and metabolism.

Step 5 — Microbial biomass and biofloc develop

Under suitable conditions, microorganisms multiply and become associated with organic and inorganic particles. Together, these microorganisms and particles form aggregates known as bioflocs.

Step 6 — Nutrients are recycled

Some nutrients become incorporated into microbial biomass and remain within the production system rather than being immediately removed through water exchange. The cycle then continues.

Feed → Animals → Waste → Microorganisms → Biofloc → Nutrient recycling

This is one of the fundamental ideas behind Biofloc Technology.

4. Why Microorganisms Matter

If you understand one thing about Biofloc, understand this:

Microorganisms are not a side effect of the system. They are part of the system's engine.

A Biofloc system can contain a diverse microbial community. Different organisms perform different functions.

Heterotrophic microorganisms

Heterotrophic bacteria use organic compounds as sources of carbon and energy. When sufficient readily available carbon is present, they can assimilate inorganic nitrogen into new microbial biomass. This process can help move nitrogen from the dissolved phase into microbial biomass. However, microbial biomass itself requires oxygen. This creates an important relationship:

More microbial growth → greater microbial oxygen demand

Nitrifying microorganisms

Nitrification is a different biological process. Nitrifying microorganisms contribute to the oxidation of:

Ammonia → Nitrite → Nitrate

Nitrification can therefore play an important role in nitrogen transformation in Biofloc systems. It also consumes alkalinity and requires oxygen.

This means nitrogen management is closely connected to:

• oxygen
• alkalinity
• pH
• microbial activity

Algae

When sufficient light is available, algae and other photosynthetic organisms can become an important part of the microbial community.

They can:

• assimilate nutrients
• contribute to microbial biomass
• participate in the food web
• influence oxygen dynamics
• influence water chemistry

However, not every Biofloc system has the same algal component.

Indoor systems with limited light can have very different microbial communities from outdoor systems exposed to sunlight.

Protozoa and other organisms

Biofloc is also home to organisms such as protozoa and other microorganisms. They participate in the microbial food web by consuming bacteria, algae and other particles. The result is therefore much more complex than simply:

"Good bacteria in the water."

It is better understood as:

A dynamic microbial food web.

5. Carbon and Nitrogen

One of the most important concepts in Biofloc Technology is the relationship between carbon and nitrogen. Feed is a major source of nitrogen entering an aquaculture system. Microorganisms, particularly heterotrophic microorganisms, require carbon to grow. When sufficient readily available organic carbon is present, microbial assimilation of inorganic nitrogen can be stimulated.

This creates an important relationship:

Feed → Nitrogen input → Microbial demand → Carbon requirement

This is why carbon management should not be considered separately from feeding.

6. What Is the C:N Ratio?

The carbon-to-nitrogen ratio, commonly abbreviated as C:N, is frequently used to describe the relationship between carbon and nitrogen available to microorganisms.

You will often encounter recommended ratios such as:

• 10:1
• 15:1
• 20:1

However, there is no universal C:N ratio that automatically produces a successful Biofloc system.

The appropriate carbon input depends on factors such as:

• feed protein concentration
• feed quantity
• carbon source
• carbon availability
• existing organic matter
• microbial community
• temperature
• oxygen availability
• system maturity
• system design

Another important consideration is that C:N can be calculated in different ways.

A C:N ratio based on total nutrients is not necessarily equivalent to a ratio based on readily available carbon and feed-derived nitrogen.

Therefore:

C:N should be treated as a management concept, not a magic number.

A deeper discussion of carbon sources and C:N calculations belongs in a dedicated article.

7. Carbon Sources

Biofloc systems can use different organic carbon sources.

Examples include:

• molasses
• sugar
• starch-based materials
• rice bran
• agricultural by-products
• formulated carbon sources

Different carbon sources behave differently.

They can vary in:

• carbon concentration
• biodegradability
• release rate
• nutrient composition
• microbial accessibility

A highly soluble carbon source can become rapidly available to microorganisms.

A more complex substrate may become available more gradually.

Therefore:

Carbon management is about more than simply choosing a quantity of carbon.

The source, availability and response of the microbial community all matter.

8. Oxygen: The Foundation of Biofloc

Oxygen is one of the most critical resources in Biofloc aquaculture. Both the cultured animals and microorganisms consume oxygen. As microbial activity and organic loading increase, oxygen demand can increase as well. This means aeration is required for two major reasons:

1. Oxygen supply

Aeration provides oxygen for:

• shrimp
• fish
• bacteria
• other microorganisms

2. Mixing

Aeration helps keep:

• microbial aggregates
• organic particles
• suspended solids

in motion.

Without sufficient mixing, particles can settle and local differences in oxygen and organic loading can develop.

Therefore:

Aeration is part of the biological infrastructure of a Biofloc system.

9. Oxygen Demand and Feeding

Feeding has a direct relationship with oxygen demand.

A simplified sequence is:

More feed

↓

More organic matter and nitrogen

↓

More microbial substrate

↓

Potentially more microbial growth

↓

Higher microbial respiration

↓

Higher oxygen demand

This does not mean that increasing feed is automatically harmful.

It means that the system must have enough capacity to process the additional biological load.

That capacity depends on:

• aeration
• microbial maturity
• temperature
• solids
• carbon availability
• biomass
• system design

This is one reason why feeding decisions in Biofloc should not be made independently from system capacity.

10. Water Quality in Biofloc Systems

Biofloc Technology does not eliminate water-quality management.

In fact, because Biofloc systems contain active microbial communities and often operate at high biomass, water-quality monitoring is particularly important.

Key parameters include:

• dissolved oxygen
• temperature
• pH
• TAN
• ammonia
• nitrite
• nitrate
• alkalinity
• suspended solids
• salinity

But these parameters should not be interpreted independently.

11. Dissolved Oxygen

DO is one of the most important measurements in a Biofloc system.

If oxygen becomes limiting:

• animals can become stressed
• feeding can decline
• microbial processes can change
• organic matter decomposition can become less efficient
• system stability can deteriorate

The risk is particularly important in systems with:

• high stocking density
• high feeding rates
• high microbial biomass
• high suspended solids
• high temperatures

A professional Biofloc system should therefore consider:

• sufficient aeration
• good air distribution
• backup aeration
• emergency power
• regular equipment inspection
• redundancy where appropriate

A power failure can become a serious biological emergency.

12. Temperature

Temperature influences:

• animal metabolism
• feed consumption
• growth
• microbial activity
• oxygen solubility
• ammonia chemistry

As temperature increases, oxygen solubility generally decreases while biological activity can increase.

This creates an important relationship:

Higher temperature → lower oxygen solubility + potentially higher oxygen demand

Temperature should therefore always be considered together with dissolved oxygen.

13. pH

pH influences both animals and microorganisms.

It also affects the balance between:

NH₃

and

NH₄⁺

At higher pH and temperature, a greater proportion of TAN can be present as the more toxic un-ionized ammonia form, NH₃.

Therefore, a TAN measurement without pH and temperature does not provide the complete picture of ammonia risk.

pH should be interpreted together with:

• TAN
• temperature
• alkalinity
• DO
• salinity
• system maturity

14. TAN and Ammonia

TAN, or Total Ammonia Nitrogen, represents the combined concentration of:

• NH₃
• NH₄⁺

The relative proportion of these forms changes with environmental conditions.

This means:

TAN is not the same thing as toxic ammonia.

A TAN measurement should therefore be interpreted alongside pH and temperature, and where relevant, salinity.

The biological processes controlling ammonia also matter.

Increasing TAN can indicate that nitrogen input is exceeding the current capacity of the microbial system to process it.

15. Nitrite

Nitrite is an intermediate compound in the nitrogen cycle.

It can accumulate when ammonia oxidation is occurring but subsequent nitrite oxidation is not keeping pace.

Nitrite problems can occur particularly during:

• startup
• rapid increases in feeding
• increases in biomass
• microbial disturbances
• changes in oxygen availability
• changes in environmental conditions

Nitrite should therefore be monitored as part of the complete nitrogen cycle rather than as an isolated parameter.

16. Nitrate

Nitrate is generally less acutely toxic than ammonia or nitrite.

However, in low-exchange or zero-exchange systems, nitrate can progressively accumulate.

This means that a Biofloc system still needs a long-term nitrogen management strategy.

Potential management pathways include:

• water exchange
• solids removal
• plant uptake
• algal uptake
• denitrification
• other nutrient-removal processes

Biofloc therefore does not make nitrogen disappear.

It changes how nitrogen moves through the system.

17. Alkalinity

Alkalinity provides buffering capacity and is important for maintaining pH stability.

It is particularly important when nitrification is occurring because nitrification consumes alkalinity.

A simplified relationship is:

Nitrification → alkalinity consumption → reduced buffering capacity → potential pH decline

If alkalinity becomes too low, pH can become more difficult to stabilize.

This is why alkalinity should be monitored as part of Biofloc system management.

18. Biofloc and Suspended Solids

Suspended solids are an important component of many Biofloc systems.

However:

More floc does not automatically mean a better system.

Excessive solids can increase:

• oxygen demand
• organic loading
• turbidity
• management difficulty
• animal stress

Too little microbial biomass can also be problematic if the system does not have sufficient biological capacity.

The goal is therefore not maximum floc.

The goal is:

A stable and functional microbial community at an appropriate solids concentration for the system.

This is why solids management is an important part of professional Biofloc farming.

19. Feeding and Biomass

Feeding is one of the strongest drivers of a Biofloc system.

Every feeding event introduces:

• nutrients
• organic matter
• nitrogen
• carbon

This means feeding affects much more than animal growth.

Consider:

More feed

↓

More nutrient input

↓

More microbial substrate

↓

More microbial activity

↓

Potentially more oxygen demand and solids

The appropriate feeding rate therefore depends on more than a feeding table.

Farmers should consider:

• estimated biomass
• survival
• growth
• feeding response
• animal behaviour
• water quality
• oxygen
• solids
• system maturity

20. Feed Is Both Food and a Biological Input

This is one of the most important concepts for a Biofloc farmer to understand.

Feed is simultaneously:

Animal nutrition

and

A biological input into the microbial system.

The farmer therefore needs to ask two questions:

How much feed do the animals need?

and:

How much biological load can the system process?

As biomass increases, feeding generally increases.

The microbial system must be capable of processing the additional load.

This is why feeding, water quality, aeration and microbial activity should always be considered together.

21. Biofloc as a Nutritional Resource

Biofloc is not only relevant to water quality.

Microbial biomass can also become part of the nutritional environment of cultured animals.

Biofloc can contain:

• microbial protein
• lipids
• minerals
• vitamins
• microbial metabolites
• other nutrients

Shrimp and fish may consume microbial aggregates and associated organisms.

However, the nutritional composition of biofloc varies according to:

• microbial community
• carbon source
• salinity
• system age
• algae
• feed inputs
• environmental conditions

Biofloc should therefore not automatically be considered a complete replacement for formulated feed.

Instead, it can be viewed as an additional nutritional component of the culture ecosystem.

22. Establishing a Biofloc System

A new Biofloc system does not behave like a mature system.

During startup, microbial populations develop and the biological capacity of the system changes.

A startup plan should consider:

• tank design
• aeration
• mixing
• carbon source
• microbial establishment
• feeding
• solids management
• alkalinity
• monitoring
• backup systems

The objective is not simply to produce visible floc.

The objective is to establish a stable microbial ecosystem capable of processing the biological load generated by the cultured animals.

23. System Maturity

Microbial communities change over time.

A newly established system can therefore behave very differently from an established system.

During development, farmers may observe changes in:

• TAN
• nitrite
• nitrate
• pH
• alkalinity
• oxygen demand
• solids
• microbial activity

Some fluctuations may be part of normal biological development.

Others may indicate that the system is becoming unstable.

This is why monitoring trends is more useful than looking at individual measurements alone.

A mature Biofloc system should not necessarily have a particular appearance.

Instead, maturity should be evaluated by biological stability and system performance.

24. Managing Solids

Biofloc systems are designed to retain microbial biomass, but that does not mean solids should accumulate indefinitely.

As organic matter and microbial biomass increase, the farmer may need to remove or manage solids.

The appropriate approach depends on:

• system design
• stocking density
• feeding rate
• solids concentration
• species
• tank geometry
• aeration
• production strategy

Solids management can therefore be an integral part of Biofloc system design.

The goal is to maintain sufficient microbial biomass while preventing excessive organic accumulation.

25. Monitoring a Biofloc System

A professional Biofloc operation should generate data.

Useful measurements and records include:

• feed input
• estimated biomass
• survival
• average body weight
• temperature
• DO
• pH
• TAN
• nitrite
• nitrate
• alkalinity
• salinity
• suspended solids
• carbon additions
• microbial products
• water exchange
• animal observations

Over time, these records become extremely valuable.

They allow farmers to identify relationships such as:

Feed increase → TAN response

Carbon addition → TAN response

Carbon addition → solids response

Temperature increase → DO response

Feeding increase → oxygen demand

Alkalinity decline → pH response

This turns Biofloc management from guesswork into data-driven biological management.

26. Monitor Trends, Not Just Numbers

A single measurement is a snapshot.

A series of measurements is a trend.

Instead of asking:

"Is my pH okay today?"

ask:

"What has happened to my pH during the last seven days?"

The same principle applies to:

• TAN
• nitrite
• nitrate
• alkalinity
• DO
• temperature
• solids
• salinity

A stable value is often more useful than a perfect value that fluctuates dramatically.

This leads to one of the most important principles of Biofloc management:

Stability is often more important than chasing individual target numbers.

27. Change One Variable at a Time

Biofloc systems contain many interacting processes.

If you simultaneously:

• increase feed
• add carbon
• add probiotics
• increase temperature
• change aeration

and the system subsequently improves or deteriorates, it can be difficult to determine why.

Where practical, controlled changes make it easier to understand cause and effect.

This is particularly important when developing a new production protocol.

A farmer who carefully records interventions and system responses gradually develops something extremely valuable:

A biological understanding of how their own system behaves.

28. Do Not Chase Numbers Blindly

A common mistake in aquaculture is to see a parameter outside a preferred range and immediately add something to correct it.

But the correct response depends on the cause.

For example:

High TAN

may be related to:

• increased feeding
• excessive biomass
• insufficient microbial capacity
• low oxygen
• poor mixing
• microbial disturbance
• temperature
• pH
• solids
• insufficient carbon availability

Adding carbon may be appropriate in one situation.

It may be inappropriate in another.

Biofloc management is therefore about understanding why a parameter changed, not simply trying to force it back to a target number.

29. Common Biofloc Mistakes

Mistake 1: Thinking Biofloc Means Brown Water

Visible floc does not prove that a system is healthy.

Mistake 2: Adding Carbon Without Understanding the System

More carbon can mean more microbial growth and potentially more oxygen demand and solids.

Mistake 3: Ignoring Oxygen

A visually impressive Biofloc system with insufficient aeration is still an unstable system.

Mistake 4: Feeding Only According to a Table

Feeding tables should be combined with biomass estimates, animal response and water-quality observations.

Mistake 5: Assuming More Floc Is Better

The goal is functional microbial biomass, not maximum microbial biomass.

Mistake 6: Treating Probiotics as a Substitute for System Management

Microbial products cannot replace sufficient oxygen, appropriate feeding, solids management and proper system design.

Mistake 7: Copying Another Farm's Numbers

A carbon dose, stocking density or solids level that works in one system may not work in another.

Mistake 8: Assuming Every Biofloc System Should Look the Same

A Vannamei nursery, Vannamei grow-out system, tilapia system, freshwater system and marine system can all have very different biological characteristics.

30. Biofloc Is Not One Recipe

Perhaps one of the most important lessons for beginners is that there is no universal Biofloc recipe.

Different systems have different:

• species
• life stages
• stocking densities
• feed compositions
• temperatures
• salinities
• tank designs
• aeration systems
• carbon sources
• microbial communities
• solids concentrations
• production objectives

Therefore, a protocol developed for one farm should not automatically be copied to another farm.

Biofloc Technology is better understood as a framework for biological management.

The farmer must adapt the framework to the specific system.

31. Biofloc and Water Exchange

One of the major attractions of Biofloc Technology is the potential to operate with low or limited water exchange.

This can provide potential benefits including:

• lower water consumption
• reduced nutrient discharge
• greater control over the culture environment
• potential biosecurity advantages
• suitability for areas with limited water availability

However, low water exchange does not mean that nutrients disappear.

Nutrients still need to be:

• transformed
• incorporated into biomass
• removed with solids
• harvested as animal biomass
• otherwise managed

Therefore:

Biofloc does not eliminate waste. It changes how waste and nutrients are managed.

32. Biofloc and Biosecurity

Reduced water exchange can potentially reduce the introduction of organisms from external water sources.

However, Biofloc systems are not automatically biosecure.

Pathogens can still enter through:

• animals
• water
• feed
• equipment
• personnel
• shared tools
• contaminated surfaces

Biosecurity therefore remains an essential part of farm management.

A healthy microbial community also does not guarantee the absence of pathogens.

Biofloc is a biological system, not a replacement for biosecurity protocols.

33. The Biofloc Mindset

The biggest change when moving from conventional aquaculture to Biofloc is often the way the farmer thinks about waste.

Traditional thinking may be:

Waste needs to be removed.

Biofloc thinking becomes:

Can nutrients be safely transformed, recycled or removed within the system?

This does not mean that all waste should remain in the tank.

It means that the farmer actively manages the biological pathways through which nutrients move.

You are not simply managing:

shrimp

or:

water

or:

feed

individually.

You are managing:

Animals + Microorganisms + Nutrients + Oxygen + Water Chemistry + Solids

as one interconnected system.

That is the Biofloc mindset.

34. The Five Principles of Biofloc Technology

If you remember only five things from this guide, remember these.

1. Biofloc is an ecosystem

You are managing microorganisms as well as cultured animals.

2. Carbon and nitrogen are connected

Feeding and carbon management influence the same biological system.

3. Oxygen is fundamental

Aeration supports both the cultured animals and the microbial community.

4. Water quality is interconnected

pH, temperature, TAN, ammonia, nitrite, nitrate, alkalinity, DO and solids should be interpreted together.

5. Stability beats extremes

The goal is not maximum floc, maximum feed or maximum stocking density.

The goal is a stable biological system capable of continuously processing the load placed upon it.

Conclusion

Biofloc Technology is fundamentally about managing biology.

Instead of relying primarily on water exchange to remove nutrients, Biofloc systems use microbial communities to transform and recycle a portion of the organic matter and nitrogen generated within the culture environment.

The process involves far more than bacteria.

It involves an interconnected ecosystem of:

Animals

Microorganisms

Carbon

Nitrogen

Oxygen

Solids

Water chemistry

Feeding

Biomass

When these components remain within the system's biological capacity, Biofloc can provide a powerful approach to intensive aquaculture.

When the biological load exceeds that capacity, instability can develop.

The most successful Biofloc farmers therefore do not simply follow a recipe.

They:

Measure.

Observe.

Record.

Understand cause and effect.

Make controlled adjustments.

And most importantly:

They manage the ecosystem, not just the water.

Continue Your Biofloc Journey

This article provides an introduction to the fundamentals of Biofloc Technology.

The Biofloc Knowledge Base goes deeper into individual aspects of the system, including:

• Water Quality
• Microbiology
• Carbon & C:N Ratio
• System Design
• Feeding & Nutrition
• Shrimp Farming
• Biofloc Management & Troubleshooting

If you want to understand the practical side of Biofloc Technology, continue with our guides on how to start a Biofloc system, Biofloc system design, carbon management, microbial communities, water quality and feeding management.

Understand the biology. Measure the system. Manage the ecosystem.