Biofloc C:N ration and ammonia control

 

How much Molasses to be added in Biofloc tank?

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If total weight of the fish in tank is 100 kg and feed is given 4% of their body weight which is 4 kg and this feed contains 30% of protein.
1.5 kg of molasses will be added daily.

In a simpler term "molasses will be 40% of the feed”

That’s quite enough if you understand this bit, but if you still insist for more detail you are welcome to read on 

What is ammonia?

A colorless gas with a characteristic pungent smell, which dissolves in water to give a strongly alkaline solution.

Where does ammonia come from in Biofloc tank?

Ammonia is the waste from the feed. Ammonia is excreted by fish through gills and through urine? Protein in feed is the main source of ammonia. 

 

More about ammonia

So far we understood that Ammonia is directly related to feed. Quantity of ammonia in the tank depends on the feed given to fish and the percentage of protein feed contains.

Let’s understand by example:

Let’s assume that we have 100 kg fish in the tank

Let’s assume that your daily feed which you give to fish is 4% of the total weight of fish, that will be 4 Kg.

This 4 kg feed contains 30% preteen (ie 1200 gm protein (1.2 kg protein)

16% of Protein is Nitrogen

16% of 1200 gm

192 gm Nitrogen / 100 mg fish / day

75% feed nitrogen is wasted as fish could not use it ie. 144 gm Nitrogen is deposited in water in form of ammonia.

 How ammonia is controlled in Biofloc tank?

Well.. For the beginning, only low protein feed is giving to fish, feed containing 25 – 30% protein. That won’t take care of the problem completely this will only help in producing less ammonia, it will still produce ammonia which need to be controlled through adding carbon sources.

How ammonia is converted into fish feed?

Now this is the magic of Biofloc where a waste like ammonia is converted into a protein feed for fish.

When ammonia increases in Biofloc tank, carbon is mixed in water.  This combination of ammonia and carbon create a new bacteria cell and that bacteria cell is protein feed for fish.

Now you have ammonia or waste of the fish converted into fish feed. Great FCR.

But there is a ratio of mixing carbon into water to convert ammonia into bacteria. Note down this ratio, this is very important.

C:N Ratio 1:10  ie 10 grams of carbon are needed to convert 1 gram of ammoniacal nitrogen into bacterial biomass. When bacteria produce new sell this sell will collect in a flock form that is called Biofloc.

There are also different recommendation to for perfect C:N ration ranging from 12.5:1 to 15:1

ref: https://www.aquaculturealliance.org/advocate/best-carbon-nitrogen-ratio-biofloc/

If you don’t understand any of the above detail, just remember this. Bacteria can only use ammonia and carbon when mixed in proper proportion and that ratio is 1: 10

How to calculate ammonia in water?

The scale used in testing ammonia is PPM / per liters or Mg / per liters. PPM stand for parts per million.

Dissolved oxygen

Don’t forget to check our blog about DO (dissolved oxygen) very important parameter of water maintenance in Biofloc

Keep testing ammonia

There are two type of ammonia found in water.

1st type is ionized NH4+ this is NOT harmful for fish

2nd form is NH3, This is unionized ammonia also known as free ammonia. This is harmful for fish. 

It should be under 0.05 PPM or Mg/ liters. Anything above this limit, result in the stress in fish and gills start getting damaged.

And level of NH3 up to 2 PPM or Mg / liters will result in fish mortality. Best scenario is zero PPM, that is practically not possible.

There is one more point to remember. There is difference in tolerance level of fish in terms of ammonia in water. For example Tilapia ammonia tolerance is higher than IMC.

How to test ammonia level

All available test kits for ammonia can only TAN (Total Ammonia Nitrogen) in the water.

NH3 depends on PH level and temperature of water; it increases with the increase of temperature and PH.

Following values should be known to find NH3.

1.       Value of TAN

2.       Temperature

3.       PH level

Once these there parameters value are find out. NH3 chart is used to find NH3.

Refer to the figure 1.1.2

Find NH3 in 3 easy steps

Step 1

Find PH value and temperature for tank

Step 2

Check value of PH and temperature in ammonia factor chart.

Setup 3

Multiply the value from ammonia factor chart with TAN value the result will be the value of NH3

Example

TAN =0.05

PH=8.4

Temperature = 27

Ammonia factor value from chart is .1495. This is multiplication factor (ref to the chart)

To find the value of NH3 multiply the TAN with ammonia factor value

NH3 = TAN X ammonia factor value

NH3 = 0.05 X .1495 = 0.007475