Biofloc Carbon & Balance C:N, Beat Ammonia
Feeds the microbes
Biofloc farming grows microbes that turn toxic ammonia into protein when the water's carbon-to-nitrogen ratio is kept high. Adding a carbohydrate (molasses) source balances the C:N — this gives the carbon source to add per day.
Balance the biofloc C:N
Next: add about 8 kg of carbon source (molasses, jaggery or starch) per day, split across feedings, to convert the 0.2 kg of ammonia-N into harmless microbial floc.
Rule of thumb: ammonia-N ≈ feed × protein% × 0.16 × 0.5. Real dosing is tuned to measured TAN; over-dosing carbon spikes oxygen demand.
Biofloc carbon — key facts
- Ammonia N
- from feed × protein × excretion
- Carbon dose
- ammonia N × C-per-N ÷ source C%
- Target C:N
- ≈ 12–20 : 1
- Molasses carbon
- ≈ 50% by weight
- Safe TAN
- keep below ~1 mg/L
- Add
- daily, dissolved, after feeding
- Works for
- tilapia, carp, catfish, shrimp
- Privacy
- Runs in your browser; nothing uploaded
Turn waste ammonia into feed, not poison
Every kilo of feed that goes into a biofloc tank releases nitrogen as ammonia, and ammonia is toxic to fish and shrimp. The biofloc trick is to feed the water's bacteria enough carbon that they grow fast and pull that ammonia into their own bodies as protein — protein the animals then graze. The lever is the carbon-to-nitrogen ratio: keep it high and the microbes consume the ammonia; let it fall and ammonia climbs and stresses the stock.
This tool gives the ammonia nitrogen produced, the carbon (molasses) source to add, the target C:N and the feed basis from your feed amount and protein. Use it to dose the tank daily, hold water quality, and recycle waste into floc protein. Pair it with the Fish Feed Requirement, Pond Aeration and Shrimp Pond Stocking calculators for a full aquaculture plan.
Control ammonia
Feed the microbes enough carbon to consume it.
Right molasses dose
Know the carbon source to add each day.
Recycle waste to feed
Turn nitrogen waste into floc protein.
Fish or shrimp
Same C:N maths for any biofloc species.
Frequently Asked Questions
What is a biofloc system?+
Biofloc is a fish or shrimp farming method that grows a dense community of beneficial bacteria and microbes in the water. By keeping the carbon-to-nitrogen (C:N) ratio high, these microbes take up toxic ammonia released by the animals and turn it into microbial protein — which the fish and shrimp then eat. It cleans the water and recycles waste into feed.
How is the carbon source dose calculated?+
First estimate the ammonia nitrogen produced from feed (feed × protein × the nitrogen and excretion fractions). Then the carbohydrate needed = ammonia N × the carbon required per unit nitrogen to reach the target C:N, divided by the carbon content of the source (molasses is roughly 50% carbon). The tool returns the carbon source — usually molasses — to add per day.
What is the C:N ratio and why keep it high?+
The C:N ratio is the balance of available carbon to nitrogen in the water. Heterotrophic bacteria need plenty of carbon to assimilate nitrogen (ammonia) into their cells. A target C:N of about 12–20:1 drives them to consume ammonia rather than letting it accumulate, so adding a carbohydrate source raises carbon and locks up the nitrogen as floc protein.
Why molasses as the carbon source?+
Molasses is cheap, readily available, dissolves easily and is rapidly used by bacteria, making it the most common biofloc carbon source. Other options include sugar, jaggery, wheat flour, rice bran or tapioca. They differ in carbon content and how fast microbes use them; molasses at roughly 50% carbon is the standard reference the calculator uses.
What ammonia level is dangerous?+
Total ammonia nitrogen (TAN) building above roughly 1 mg/L — and especially the toxic un-ionised fraction at high pH and temperature — stresses fish and shrimp, harming gills, growth and survival. The whole point of biofloc carbon dosing is to keep ammonia from accumulating by feeding the microbes enough carbon to consume it as it is produced.
How often do I add the carbon source?+
Typically the calculated carbohydrate is added daily, often split through the day or after feeding, and dissolved before adding so it disperses. Monitor TAN and nitrite, floc volume (Imhoff cone) and dissolved oxygen, and fine-tune the dose — more carbon when ammonia rises, less as the mature floc community stabilises water quality.
Does it work for both fish and shrimp?+
Yes — the C:N balance principle is the same for tilapia, catfish, carp and shrimp (vannamei). Just enter the feed amount, the feed's crude protein and your target C:N, and the tool gives the carbon source to add. Stocking density, aeration and floc management differ by species, but the carbon dosing maths is universal.
Do I still need aeration and water exchange?+
Yes — biofloc is oxygen-hungry because the microbial community and animals both consume it, so continuous strong aeration is essential. Biofloc reduces but does not always eliminate water exchange; you still manage solids (settling), pH and alkalinity. Carbon dosing controls nitrogen, but aeration and solids management keep the system healthy.
Are the doses exact?+
They're solid planning doses. Actual carbon demand shifts with floc maturity, temperature, the real protein and excretion of your feed, and the exact carbon content of your molasses batch. Start with the calculated dose, watch ammonia and nitrite closely in the first weeks, and adjust — biofloc carbon dosing is steered by water-quality readings, not set once.