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.
Reduced pond depth: Growth of algae (algae absorbed ammonia) is limited by lighting conditions. Anything that increases the light also increases the absorption of ammonia. Theoretically, algal blooms in shallow ponds will absorb ammonia more effectively in deep ponds. However, in general, deep ponds still have more benefits (eg easier to harvest fish, conserve water, stabilize temperature, reduce the effect of sediment layers between ponds).
– Increasing pond depth: Clearly, deep ponds contain more water than shallow ponds. Therefore, with a certain feeding rate, deeper ponds have lower concentrations of ammonia because of more water to dilute ammonia from fish secretions. In fact, deep ponds do not have enough water to dilute ammonia significantly as compared to the large amounts of ammonia discharged continuously by biological and non-biological abnormalities in ponds. Moreover, deeper ponds create stratification and lower layers (hypolimnions) that can concentrate ammonia and dissolved oxygen. When this water layer is mixed with surface water during convection, it can lead to water quality problems.
– Water change: Ammonia can be pushed out by changing water, although pumping large amounts of water is so expensive, time consuming, and unnecessary waste. This is also an inefficient option for ammonia management. Suppose the ammonia concentration in a 10-acre pond (4046 m2) is 1 mg / l. Ammonia concentration after pumping 500 gpm continuously for 3 days would be 0.90 mg / l, only 0.10 mg / l reduction. The effect of this work is being questioned because it does not solve the root problem. Drainage of pond water is not only ineffective, but also undesirable because of concerns about discharge from ponds into the environment.
– Use of bacteria:
+ Some believe that ammonia builds up in the pond because of the lack of necessary bacteria. If this is true, simply adding the required bacteria to the pond will solve the problem. However, research on many strains of bacteria almost always results in the same result: water quality is not affected by the addition of these bacteria.
+ The management of ponds according to current standards has created favorable conditions for bacterial growth. The activity and growth of bacteria is limited by the amount of oxygen and temperature more than the number of bacteria. In addition, bacteria (in pond water and sediment) are responsible for the decomposition of organic matter. Therefore, increasing the bacteria will promote the decomposition of organic matter, the actual ammonia concentration will increase rather than decrease.
Some species of bacteria oxidize ammonia into nitrates. Adding them also will not reduce the concentration of ammonia quickly because the bacteria must grow for several weeks before there is a sufficiently large amount to affect the level of ammonia.
– Using organic carbon sources:
+ If the dissolved oxygen levels are sufficiently dissolved, adding an organic carbon source, such as minced hay, to the intensive fishpond can reduce the concentration of ammonia. Although feeding fish is frequent, many types of bacteria in fishponds are still starved of organic carbon. Organic matter in fishponds (dead algae cells, fecal solids, and leftovers) do not guarantee optimum levels of nutrients for the bacteria to grow.
+ The reverse side of this method is very difficult to put large amounts of organic matter into the pond, while the effect on ammonia concentration is not fast. Furthermore, it would have to increase the aeration to meet the oxygen demand for the decomposition of such large amounts of organic matter.
– Addition of ion exchange materials:
Some natural materials, called zeolites, can absorb ammonia in water. This is a practical method used in aquariums or small scale ponds, which is a very good fish protection system, but not practical for large ponds.
+ Some shrimp farmers in Southeast Asia have tried to use about 200-400 kg of zeolite fertilizer for each acre (4,046 m2). However, research has proven that this practice is ineffective and has been neglected.
– How to reduce the pH:
+ In theory, adding acid (such as hydrochloric acid) to water will reduce pH. This can change the ammonia balance so that they turn into non-toxic form (NH4 +). However, large amounts of acid will be needed and will have to be rapidly mixed across the pond to prevent “hot spots” that can kill fish. Moreover, adding acid will destroy the alkalinity of the pond before the pH changes significantly. When the ammonia concentration is lowered, the treatment ponds need to be lime to restore the buffering capacity. On the other hand, working with strong acids is also a danger to labor safety and aquaculture.
+ In summary, because there are very few effective measures to overcome ammonia poisoning that occur in ponds, the key to effective ammonia management is the adoption of Good Aquaculture Practices Rules to minimize the probability of occurrence. Out problem. This means stocking fish at reasonable densities, harvesting regularly to ensure that fish are not oversized, and using good feeding practices to maximize fish feed conversion ratio (FCR).