How to control Ammonia in Black Tiger Prawn’s ponds (Part 1)

Ammonia is a toxic substance that is accumulated during the culture process. In properly managed ponds, ammonia rarely builds up to dangerous concentrations. However, ammonia can create so-called “lethal effects”, such as reduced growth, poor food metabolism and reduced immunity in low concentrations.

1. The effect of pH and temperature on ammonia

– Ammonia in water exists in either ammonia (NH3) or ammonium (NH4 +). The relative survival rates for these two forms are mainly affected by pH. Non-ionized ammonia (NH3) is toxic and prevails at high pH. Ammonium ions (NH4 +) are less toxic, predominantly at low pH. In general, when the pH is less than 8.0, the level of ammonia in the toxic form is less than 10%. This rate increases significantly when pH increases.

– In ponds, pH fluctuates by photosynthesis (increase pH) and respiration (decrease pH) of microorganisms. Thus, ammonia (NH3) increased in the late evening, while ammonium (NH4 +) predominated before sunrise until early morning.

– The ratio between NH3 and NH4 + is also influenced by temperature. With a certain pH, toxic NH3 is present in more warm water than in cold water (graph).

2. Sources of ammonia
– The main source of ammonia in ponds is the excretion of livestock. The excretory rate is directly related to the rate of feed and protein content in the feed. When the protein breaks down in the body of the animal, some nitrogen compounds break down to form proteins, some of which make up energy, and some of it through the gills that make up ammonia. Therefore, protein in feed is the source of most ammonia in the pond.

– Another source of ammonia is diffusion from sediment layers. These classes are mostly organic substances derived from algae or food supplements, solids from secretions and dead algae that settle to the bottom of the pond where they are decomposed, etc. Decomposition of organic matter This produces ammonia and diffuses into the water.

3. How to manage ammonia
– Very rarely ammonia levels become high enough to cause serious problems. However, if the problem occurs, how can it be handled? Actually there are not many ways to handle it. Theoretically, there are some ways to reduce ammonia levels, but most of the methods are only used for large ponds used in commercial growers.

Stop or reduce feeding rates: The main source of ammonia in ponds is the protein in the feed. When the protein in the feed is completely metabolized, ammonia is produced in the fish body and excreted through the gills into the pond water. It therefore seems reasonable to conclude that ammonia control can be achieved by adjusting the feeding rate or protein level in the feed. This is only true to some degree, depending on the control in the short term (days) or long term (weeks or months). In the short term, the drastic reduction in feeding rates has little direct effect on ammonia concentrations. In the long run, it can reduce the risk by adjusting both the feeding rate and the protein content. When administered with caution, it is possible to minimize the possibility of increased levels of ammonia and associated risks (disease, poor food metabolism, slow growth).

– Enhancing Aeration: NH3 is a dissolved gas, so some manufacturers believe that aeration is a way to remove ammonia, because it enhances the diffusion of ammonia from water into the air. However, research has shown that aeration is ineffective, as the amount of water affected by the aeration device is quite small relative to the total amount of water in the pond, and the concentration of ammonia in water is generally relatively Low (especially in the morning). Even so, aeration can increase NH3 concentrations, because they prevent the deposition of sediment and promote organic decomposition.

– Apply Lime: Many people think lime will reduce the concentration of NH3. In fact, using lime can make the situation much worse, by causing a sudden increase in pH, which in turn causes the ammonia to change and turn more into toxic form for fish. In addition, the amount of calcium in the lime can react with soluble phosphorus, transforming them into algae that lack the substance to grow. Therefore liming is only effective if the pond is low alkalinity. Meanwhile, most fish ponds are alkaline enough. Increasing the alkalinity above 20 mg / l (according to CaCO3) will not bring any benefits. Moreover, liming does not address the root causes of high ammonia concentrations, it only changes the volatility of the ammonia from toxic to non-toxic by regulating the high pH that usually appears in the afternoon.

– Apply phosphorus: Most ammonia is absorbed by algae. So any factor that boosts algae growth will increase ammonia absorption. This fact is the basis for the idea of ​​applying phosphorus to ponds to speed up the growth of algae, thereby reducing ammonia levels. However, under normal pond conditions algae are very dense and growth of algae is limited mainly by lighting conditions, not due to lack of nutrients such as phosphorus or nitrogen. Therefore, this measure does not work.

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