Before each crop, it is necessary to renovate the pond according to the correct technique to bring the best effectiveness and avoid unnecessary damage.
Pond bottom drying
It is necessary to wash the pond bottom after each crop, pump the sludge into the sludge pond to dry and dump. It is not advisable to pump or pour sludge onto pond banks since rainwater can bring waste back to the pond. Carry out washing and rinsing a few times until it is completely clean, then dry the pond bottom.
Drying bottom is one of the important and indispensable steps in pond improvement technique. Thoroughly renovated and well-managed pond bottom creates favorable conditions for shrimp development and growth. After each crop, the pond bottom is usually dried until the soil cracks. This technical measure helps to destroy pathogens, release toxic gases accumulated in the bottom, completely decompose wastes; facilitating watercolor, developing natural food sources in the pond. For ponds that cannot be pumped out or renovated during the rainy season, probiotics capable of killing bacteria and decomposing wastes can be used for treatment. It is necessary to run the fan continuously during microbiological treatment.
Plowing the soil of pond bottom
he popular method is dry improvement and re-plowing of ponds to promote oxidation to help organic decomposing and limit pathogens. The pond bottom soil is plowed making the soil more aerated because there are anaerobic areas due to the accumulation of organic and H2S toxic gas, except for some cases that should not be plowed and must prevent erosion when the pond bottom soil is acidic due to iron ore, as the pH can be significantly reduced.
According to experts, lime has many effects: Loosen mud, improve the air conditions at the bottom, speed up the decomposition of organic matter in the pond, release N, P, K in the mud, increase nutrition; keep the pH stable. Plow bottom soil with a depth of about 5 – 10 cm, then lime CaO at a dose of about 5 – 10 kg/100 m2 to stabilize the pH of the pond bottom, destroy pathogens from the previous crop. and decomposes all toxic gases (depending on soil pH and acidity of the soil)
Soak and rinse
Apply to ponds contaminated with alum or with diseased shrimp during the crop. For ponds with soil contaminated alum, spread hot lime (CaO) evenly on the bottom, then soak for 2-3 days under 40 – 50 cm of water and then discard. In case the pond is contaminated with EHP spores, the amount of lime that needs to be used is 6 tons/ ha. If the pond has been infected with diseases in the previous crop, it is possible to combine additional treatment with disinfectants after the water has been taken. Repeat this cycle 2-3 times. To ensure effectiveness, the soil pH or Vibrio density should be checked by the technician.
Pond need to be fertilized to make color for animals and phytoplankton to develop as a natural food source for shrimp, and at the same time limit the growth of bottom algae, create oxygen, absorb toxins arisen from excess feed, shrimp feces during the farming process. Fertilizer should be dissolved with water before spreading over the pond to avoid sedimentation at the bottom, enriching the soil and stimulating benthic algae growth. The amount of fertilizer in the pond depends on the area of the pond and the dosage of each fertilizer.
The water source must be active, not polluted, the dissolved oxygen must be> 4 mg/liter of water; pH: 7 – 8.5. Water must be filtered through the net to limit the waste and prevent natural shrimp and fish, settle for 10 – 20 days.
Transfer water from sedimentation pond to farming pond
Pump water through a filter bag with kate cloth to eliminate predators, competitive organisms or vectors carrying pathogens such as crabs, shrimps, shrimps …
Killing the trash
Run a fan for 3 consecutive days to make eggs and crustaceans fully hatched and then kill the trash with tea pulp (saponin), herb roots (rotenone) or specialized chemicals according to the manufacturer’s instructions. For the treatment of screws or bottom seaweeds, copper sulfate (CuSO4) can be used with a concentration of 2 – 3 ppm.
Two days after killing impurities, kill bacteria to eliminate pathogens in pond water. Chlorine, TCCA, BKC, potassium permanganate KMnO4, Formol, Iodine or PVP-Idodine are currently the most commonly used disinfectants. Farming areas with acute hepatopancreatic necrosis disease (EMS / AHPND) should use BKC dose of 0.3 ppm (Hoang Tung et al., 2015).