Polyaluminium chloride manufacturers share the secret of raising water first in aquaculture

It is widely known that "aquaculture starts with water quality." Water is the environment in which fish and shrimp grow, survive, and live. However, the interaction between pond sediment and water can strongly affect water quality. Therefore, to cultivate good water, one must start with pond sediment improvement and must pay full attention to pond sediment management. "A new pond thrives for three years" is a realistic portrayal of pond aquaculture. To achieve sustainable development of pond aquaculture and reasonably maintain pond soil and water resources, it is necessary to improve and restore deteriorated pond sediment. How do you restore deteriorated sediment? YishengPolyaluminium chlorideThe editor will now share with everyone:

I. Main characteristics of pond sediment

Pond sediment serves not only as a water-holding reservoir for aquaculture and a storage depot for various chemical substances, but also as a habitat for plants, animals, and microorganisms, as well as a core site for nutrient recycling. Substances continuously settle from pond water to the pond bottom, for example: suspended solids in surface runoff flowing into the pond, applied fertilizers and uneaten residual bait, and dead animals and animal carcasses in the water body. Substances may also enter the soil solid phase of pond sediment through ion exchange, adsorption, and precipitation. Substances entering the sediment may be permanently stored, or may be converted into other substances through physical, chemical, or biological methods and lost from the pond ecosystem. Organic matter deposited at the pond bottom is typically decomposed into inorganic carbon and released into the water as carbon dioxide. Nitrogen-containing compounds are denitrified by microorganisms in the pond sediment and lost to the atmosphere as nitrogen gas, while phosphorus is adsorbed by the pond sediment and buried in the deposits, entering the cycle of the available phosphorus pool. Sulfur-containing compounds produce hydrogen sulfide through the action of reducing bacteria, which then combines with metal ions in the pond sediment (iron, manganese, etc.) to form black sulfides that settle into the sediment.

Pond sediment soil is the living place for some bacteria, fungi, higher aquatic plants, small invertebrates, and other benthic organisms. In addition, crustaceans and benthic fish also spend most of their time at the bottom, and many fish even build nests and spawn at the bottom. The decomposition role of microorganisms occupies a very important position in the nutrient cycling of sediment, because through hydrolysis, organic matter is oxidized into carbon dioxide and ammonia, and other mineral nutrients are released. In this way, through microorganisms, carbon, nitrogen, and other elements are mineralized or recycled, and they can still be utilized. However, if the balanced concentration of a certain nutrient is too low, it may be unfavorable for the growth of phytoplankton, or if the balanced concentration of a certain heavy metal element is too high, it can cause poisoning in aquatic animals.

The particle size and texture of sediment soil, pH and acidity, organic matter characteristics, nitrogen concentration and carbon-to-nitrogen ratio, as well as the depth of deposits and nutrient concentrations, can all affect the management of aquaculture pond sediment. The active components of sediment soil should be clay particles with charges and enormous surface area, and organic materials with biological availability and high chemical activity. The characteristics of pond sediment are closely related to aquaculture yield, and different sediments also lead to different growth and development of aquatic animals as well as different water quality indicators.

II. Harm of pond sediment deterioration

After a period of aquaculture, a portion of residual bait, feces, fertilizers, dead algae, and other organic particles sink to the pond bottom, and dead organisms after fermentation and decomposition mix with pond bottom mud and sand to form sludge. A certain thickness of sludge can play a role in supplying fertilizer, retaining fertilizer, and regulating and buffering gradual changes in pond water quality.

The organic decaying substances in the sludge and the harmful substances produced by decomposition consuming dissolved oxygen, such as carbon dioxide, ammonia nitrogen, nitrite, hydrogen sulfide, and various organic acids, are excellent culture media for pathogenic bacteria or hiding places for various parasite eggs. Excessive sludge thickness and deteriorated sediment can cause serious harm to fish, and in most cases this harm is indirect. In ponds where feed is applied, residual feed and excretory waste from fish and shrimp cause massive reproduction of phytoplankton in the pond, and these phytoplankton control changes in dissolved oxygen in the pond. During the day, the oxygen produced through photosynthesis is greater than the oxygen consumed by respiration, so the dissolved oxygen concentration is relatively high; at night, the opposite is true. With the input of large amounts of feed, algal blooms are very common in our aquaculture process, especially in the later stages of aquaculture. In addition, if the organic matter concentration in pond sediment is too high, it will favor the formation of anaerobic conditions at the pond bottom, leading to the production of toxic microbial metabolites, and harmful substances such as ammonia nitrogen and nitrite will increase, further intensifying the pond bottom turning black and foul, deteriorating water quality, and causing massive reproduction of parasites and pathogens. Therefore, sediment, water quality, and disease are closely related.

III. Main factors of sediment deterioration

1. Incomplete pond clearing, too short pond drying time, improper drugs used for pond clearing, and excessive drug residues caused by pond clearing, etc.

2. During the aquaculture period, excessive organic matter residue and bottom hypoxia are the most important factors in sediment deterioration. Residual organic matter such as leftover bait, feces, and biological remains causes a sharp increase in biological oxygen demand and chemical oxygen demand. The dissolved oxygen at the bottom of the water body cannot satisfy the oxygen demand, thus causing hypoxia in the pond sediment, massive proliferation of anaerobic bacteria, and decomposition of bottom organic matter producing large amounts of toxic intermediate products, such as ammonia nitrogen, nitrite, hydrogen sulfide, methane, organic acids, and other harmful substances. These toxic substances have a strong toxic effect on aquatic animals, and at the same time cause massive reproduction of pathogenic bacteria and hypoxia-induced surfacing, etc.

3. Large-scale and frequent use of chemical disinfectants, pesticide insecticides, algicides, etc., thereby damaging the self-purification capacity of the water body and sediment.

IV. Poor sediment types

1. Acidic and foul-smelling, fishy-smelling sediment

Causes: Too much decaying organic matter at the pond bottom, mainly due to incomplete pond clearing, excess feed input during aquaculture, failure to take measures to improve sediment regularly, etc. In addition, insufficient oxygenation measures and failure to regularly broadcast oxygen-releasing agents result in organic matter not being fully oxidized and decomposed. [E.N.] The Symbiosis with Companion Stars Sharing Session and Winter Night Sky Observation Event came to a successful conclusion! producing large amounts of toxic intermediate products such as ammonia nitrogen, nitrite, hydrogen sulfide, methane, etc. In severe cases, the sediment will produce large amounts of harmful gases, showing a "bubbling" phenomenon.

2. Hardened sediment

Causes: Repeated large-scale use of chemical fertilizers to fertilize water, excessive use of copper sulfate insecticide and algicide, large-scale use of quicklime and other drugs, causing sediment hardening. The exchange of gases and nutrient elements between sediment and water body is blocked, the buffering capacity of the water environment is weakened, water quality changes unpredictably, and aquatic animals are prone to stress reactions.

3. "Mud skin" sediment

Causes: Large amounts of aged and dead algae and suspended colloidal deposits settle at the bottom. After microbial action, they become floating scum and form large amounts of foam on the water surface, etc.

4. "Filamentous algae" sediment

Causes: The exchange of nutrient elements between sediment and water body is blocked, resulting in imbalance or deficiency of nutrient elements in the water body, appearing as "algae collapse" and "water turnover" (water quality becoming clear overnight). The water quality is too lean and clear to the bottom, and filamentous algae and blue-green mud moss at the bottom reproduce in large numbers.

5. "Turbid" sediment

Causes: Excessive organic matter residue that cannot be fully oxidized and decomposed is released in colloidal form and suspended in the water body, causing water quality to become "turbid"; or excessive aquaculture density causes aquatic animals to constantly disturb the bottom, causing water quality to become "turbid"; or heavy rain carries large amounts of clay slurry, causing water quality to become "turbid." "Turbid" water quality, Hong Kong's 30-year hit song medley, we all grew up listening to these Hong Kong pop songs! suspended and settled to the bottom, will inevitably cause the sediment to become "turbid"; in addition, "turbid" water quality will shield algal photosynthesis, weakening the self-purification capacity of the water body, causing massive reproduction of pathogenic microorganisms and resulting in disease.

6. "Stealth death" sediment

Causes: Due to long-term hypoxia at the bottom, harmful substances such as ammonia nitrogen, nitrite, hydrogen sulfide, methane, and organic acids accumulate excessively, causing aquatic animals to die from poisoning at the bottom. During harvest, large amounts of dead carcasses are found at the bottom.

V. Pond sediment improvement methods

In production, more attention is paid to water body improvement. There is a saying of "watching the water to raise fish," but little attention is paid to whether the bottom water is hypoxic and whether the sludge is foul-smelling and black. The fish "surfacing" or "pond turnover" that we often encounter are mostly the result of sediment deterioration. If the sediment is good, even under abnormal weather such as "heavy rain," it will not cause a rapid decrease in dissolved oxygen or a rapid increase in harmful substances. We know that low dissolved oxygen not only makes it difficult for aquaculture animals to survive but also affects the feeding and digestion rate of aquaculture animals. It can also cause an increase in harmful reducing substances (ammonia nitrogen, sulfides, etc.) in the water body and an increase in pathogenic bacteria, thereby affecting the stability of the water body and the growth and disease resistance of aquaculture animals. Therefore, sediment restoration and improvement are of great significance.

1. Physical methods

Pond clearing and dredging are normally carried out in winter or early spring and other slack production seasons. Most adopt the method of first draining the pond water, then using a hydraulic pond-digging unit to clear the sludge just like digging a new pond. This method has low cost and strong adaptability, but the operation requires a water source and a relatively large wasteland or shallow beach for discharging the mud slurry and allowing it to settle. Production practice has proven: the sludge thickness at the bottom of silver carp and bighead carp ponds should be 20 cm to 40 cm; the sludge at the bottom of grass carp, bream, and common carp ponds should preferably be 10 cm to 15 cm. Therefore, to maintain good water quality, every 12 years, 10 cm to 20 cm of dark black sludge should be removed. The pond bottom then undergoes freezing and sun exposure ("winter drying") to promote the decomposition of organic matter and destroy pathogens and other harmful organisms. During this period, work such as repairing and reinforcing the pond, plugging leaks, maintaining gates, and removing weeds can also be carried out.

In production, it is sometimes necessary to carry out dredging without draining the pond water. The dredging machines currently in use can be roughly divided into two types: boat-type dredging machines and submersible dredging machines. The main working parts of the boat-type dredging machine are all installed on the boat, with only the suction head submerged underwater. It can remove sludge from the pond bottom during the aquaculture period, and the suction and discharge operation is continuous. All working parts of the submersible dredging machine are submerged to the pond bottom, walking on the surface of the sludge while performing suction operations. However, because the entire machine operates underwater, it has high requirements for waterproof sealing of the power engine, high technical difficulty in maintenance, and is inconvenient for users to maintain and repair on their own.

In addition to dredging, frequently stirring the pond bottom, loosening the sludge at the pond bottom, and mixing the pond water from top to bottom can also promote the decomposition of organic matter at the pond bottom and re-release nutrient salts deposited in the sludge, restoring the balanced distribution of nutrients in the upper and lower water layers of the pond, promoting the growth and reproduction of plankton, thereby avoiding pond bottom aging; aeration through turning on aerators can also improve the bottom environment and slow down the blackening process.

2. Chemical methods

The most commonly used chemical method is pond clearing with quicklime. Quicklime undergoes a chemical reaction upon contact with water, releasing large amounts of heat energy, neutralizing various organic acids in the sludge, and changing the acidic environment, thereby achieving the effects of eliminating pests, killing bacteria, fertilizing, and improving sediment and water quality. When using it, the pond can be cleared either dry or with water. Clearing with water is generally done in ponds with low total alkalinity, total hardness, and pH, applying lime in a timely and reasonable manner; however, if the calcium ion concentration in the pond water and sediment is relatively high and alkalinity is relatively high, quicklime need not be applied; in aquaculture ponds poor in organic matter, quicklime should not be applied alone, otherwise it will intensify the decomposition of organic matter, leaving even less organic matter accumulated, further reducing pond fertility, and making recovery even more difficult.

In addition to quicklime, chemical composite sediment improvers can also be used. For example, a white granular "bottom water quality improver" whose main component is calcium peroxide can rapidly increase oxygen when put into water, promote nitrification, reduce the content of ammonia nitrogen, nitrite, and sulfide in water, and also supplement calcium needed for biological growth, making the sediment loose and breathable and promoting complete decomposition of organic matter. At present, a new type of nitrite ion removal agent?? nitrite chelating agent (BRT) and its salts can degrade nitrite nitrogen and ammonia nitrogen in pond water, chelate organic matter in pond water, and eliminate pollution from heavy metal ions contained in pond water and pond bottom, etc. It can be used as a pond soil improver, sediment improver, and sediment activator. Represented by flocculants such as polyaluminium chloride, aluminum sulfate, and alum, after use the water body will stratify, the middle and upper water body will become clear, and there will be large amounts of cloud-like flocculent gel at the bottom layer.

3. Biological methods

Using organisms to restore aquaculture pond sediment and reduce the accumulation of organic matter in the sediment can also achieve significant results. According to reports, transplanting benthic organisms such as sandworms into aged and polluted shrimp ponds and cultivating them into dominant populations can consume large amounts of residual bait, feces, and other biological remains and organic debris in the shrimp pond, slowing down the accumulation of organic matter at the bottom of the shrimp pond. Moreover, sandworms live in burrows, and the continuous movement of their bristles can form small water flow circulations, increasing dissolved oxygen in the sediment.

Microbial preparations such as photosynthetic bacteria and composite probiotics can also improve pond sediment. Photosynthetic bacteria can reproduce at the pond bottom where light is dim and organic matter, hydrogen sulfide, etc. are abundant, and use these substances to build themselves, while they themselves are preyed upon by other animals, forming an important link in the material cycle and food chain in aquaculture ponds. Therefore, photosynthetic bacteria can play a relatively obvious role, especially in closed aquaculture ponds where the pond bottom is seriously polluted or water cannot be exchanged due to poor water quality. Composite microbial sediment improvers can exert the synergistic effects of various bacterial species, eliminating hidden dangers that affect sediment deterioration, such as residual bait, excreta, and animal and plant carcasses, in a timely manner. They not only improve sediment and water quality but also control the spread and diffusion of pathogenic microorganisms and their diseases.

4. Others:

The rate of sludge deposition is directly related to feeding management measures such as fertilization and feed application. In production, try to fertilize based on water observation and avoid excessive application; carry out reasonable mixed culture and dense culture according to the principle of ecological complementarity; flexibly control the feeding amount according to season, weather, growth conditions, and changes in the water environment; add phagostimulants and growth promoters to feed to enhance the appetite of aquatic animals, promote the absorption and transformation of feed nutrients, reduce the feed conversion ratio, and solve pollution of sediment and water quality by excreta from the source; prevent massive growth of aquatic plants (especially filamentous algae), and promptly remove excessive or dead aquatic plants to prevent rotting and deterioration; where conditions permit, sprinkle iron-making furnace slag (generally 1.5 kg/m3) over blackened areas to delay the blackening process and reduce harm.

In addition, if the dry pond period is relatively long, consideration can be given to continuous cropping of aquaculture and crops. This can allow the sludge to dry more thoroughly. Relying on the well-developed root systems of terrestrial crops, the soil can fully contact the air, which is conducive to the mineralization and decomposition of organic matter and better improves the pond bottom. At the same time, the economic value of the crops themselves can also be obtained. In addition, the green crops and forage grass grown can also serve as excellent green manure for the pond and feed for fish.

The buffering capacity, self-purification capacity, production function, and stress resistance of pond sediment are key to the success or failure of pond aquaculture. "Success lies in the sediment, failure lies in the sediment" is not an exaggeration at all for the pond aquaculture industry. To achieve sustainable development of the pond aquaculture industry and overcome continuous cropping obstacles, regular improvement of pond sediment needs to attract sufficient attention from pond aquaculture practitioners.

VI. Common sediment improvers

1. Adsorption type: such as zeolite powder, medical stone, activated carbon, etc. They only simply physically adsorb harmful substances such as ammonia nitrogen, nitrite, and organic matter in water. After use, the water will become clearer, but the characteristics of the harmful substances themselves are not changed; they are only diluted within it, and settling to the pond bottom aggravates bottom foulness.

2. Flocculation type: represented by flocculants such as polyaluminium chloride, aluminum sulfate, and alum. After use, the water body will stratify, the middle and upper water body will become clear, and there will be large amounts of cloud-like flocculent gel at the bottom layer, so after use in production it will also aggravate hypoxia at the bottom layer.

3. Ion exchange type: such as products mainly containing EDTA or sodium thiosulfate (hypo), used to reduce cationic harmful substances such as ammonia nitrogen and heavy metals in water or at the bottom layer, or used for detoxification in cases of poisoning by positive oxides such as bromine-, chlorine-, and iodine-containing compounds and potassium permanganate. The effect is relatively ideal, but the effect on negatively charged acidic harmful substances (organic matter) in water or at the bottom layer is very poor.

4. Live bacteria degradation type: at present, there are many biological sediment improvers on the market, mainly composed of Bacillus subtilis, nitrifying bacteria, denitrifying bacteria, and some zeolite powder as a live bacteria carrier, sometimes with sodium humate, trace elements, etc. added.

One category is mainly composed of oxygen-consuming live bacteria such as Bacillus, nitrifying bacteria, and denitrifying bacteria, which must be in a high-oxygen environment to exert their functions. Moreover, this type of biological sediment improver will consume large amounts of oxygen during use, especially in aged bottom ponds and ponds without aeration equipment, so it should be used with caution. The other category is mainly composed of anaerobic bacteria such as photosynthetic bacteria, lactic acid bacteria, and yeast. Because they do not consume oxygen, their side effects are not taken seriously by people. Taking yeast as an example, its sediment improvement process is a fermentation process. Although this fermentation is anaerobic fermentation, the fermentation process is a process of energy and heat production. This bottom heat caused by fermentation, and the hypoxia caused by bottom heat, will become more significant and more harmful as organic matter such as residual bait and feces at the bottom layer increases. Therefore, in production, when using live bacteria sediment improvers, use should be avoided as appropriate during high-temperature rainy seasons. In addition, excessive organic matter at the bottom layer of many old ponds will not only cause bottom foulness but also breed large numbers of protozoa (such as ciliates, rotifers, cladocerans, and copepods). If live bacteria are used to improve the sediment, these zooplankton will directly ingest the live bacteria as food, thereby accelerating the reproduction of zooplankton. In addition, algae compete with autotrophic microorganisms such as photosynthetic bacteria and nitrifying bacteria, so when algae are excessive, it is not conducive to the reproduction of these bacteria, thereby affecting the sediment improvement effect.

5. Chemical degradation type: mainly various halogen types, alkaline metal salts and other oxidants, as well as some surfactants. This type of sediment improver is all chemical degradation type. For products of the same type, the good or bad is generally judged by how quickly or slowly they release upon hydrolysis. The faster the hydrolysis, the greater the irritation; the slower the hydrolysis, the less the irritation. In addition, this type of product is not affected by environmental factors such as weather and water temperature, and these products are relatively commonly used in production.

VII. Precautions

1. Before using various sediment improvers, turn on the aerator 12 hours in advance, or use 1 kg of oxygen-releasing agent per mu, broadcast it over the whole pond, and then use the sediment improver for better results.

2. Strictly use various sediment improvers according to the instructions. If one application does not show obvious results, use once more the next day. Never use an excessive amount at one time.

3. Never use alum or some aluminum-containing products to improve water quality.