How to fix alum contaminated pond

(Baonghean) - At this time, aquaculture ponds have large changes in pH after rains. Especially in areas with soil contaminated with alum, when the rain washes away the alum, the pH in the pond changes suddenly, affecting the health of livestock, possibly causing mass deaths of shrimp and fish. Therefore, treating alum-contaminated ponds at this time is very necessary.

Spread quicklime to fix alum in shrimp pond.

Symptoms of ponds contaminated with alum

Acid sulfate soil is often found in mangrove areas, alluvial plains and low salinity areas, pond bottoms have many rotten leaves and clay. After rains, ponds show signs of acid sulfate contamination such as clearer water or light tea color, a pale yellow film floating on the water surface, and no algae growth.

For fish ponds, when the alum level is high, the fish skin turns dark black, the fish become thin and grow slowly, if the pH drops too low, there will be a phenomenon of mass fish deaths without clear cause.

For shrimp ponds, it is observed that the entire body of the shrimp changes from a clear color to a light yellow to a dark yellow, the color of tea water, touching the shrimp shell feels harder than usual, at the same time, the shrimp gills turn yellow and harden. Shrimp have difficulty molting and start to stop eating after prolonged rains, if the pond is heavily alum, the shrimp will drift to the shore and die sporadically, due to suffocation because alum sticks to the shrimp gills, hindering the shrimp's breathing process.

How to handle

For ponds with soil contaminated with alum, when renovating, it is necessary to use litmus paper to check the pH of the pond bottom or chew betel and spit it into the mud at the bottom of the pond. If the betel juice is still bright red, it proves that the pH is within the appropriate range (7 - 8); if the betel juice changes from red to dark or purple, it proves that the bottom is contaminated with alum. It is necessary to increase the amount of agricultural lime CaO applied to the pond, at a dosage of 10 - 15 kg/100 m2.

It is necessary to use a tarpaulin to cover the pond bottom to the surrounding bank to prevent rainwater from seeping through the bank and overflowing, or build a soil berm to prevent rainwater from flowing directly into the pond. After it rains, it is necessary to lift the upper flap of the drain to drain some of the water at the surface to avoid pH shock for shrimp and fish.

Compact the bank firmly and keep the pond water level balanced with the surrounding ditch or pond, avoid low water level, alum will leak, seep into the pond with water. During the farming process, use lime powder or slaked lime diluted with water and sprinkle evenly into the pond, dosage 1 - 2 kg/100 m2, periodically 15 - 20 days/time, before it rains, lime should be spread around the pond bank with a dosage of 2 kg/100 m2. Regularly use litmus paper to measure the pH of the water, the appropriate level for shrimp and fish to grow and develop is 6.5 - 7.5, if lower than the allowable threshold, lime must be sprinkled immediately with a dosage of 1 - 2 kg/100 m2.

In alum ponds, the water is highly clear, the pond is poor in nutrients, algae do not grow, so you should replace the old water and add new water or use dolomite lime at a dosage of 20 - 30 kg/1,600 m2, fertilize every 2 days, within the first 20 days to create and maintain the water color of the pond.

For shrimp ponds, when the pH is low, in addition to using lime, farmers can also use Sitto Thio 5000 product, dosage 1 liter/300 m3 of water and combine with Zeolite 10 kg/1,000 m3 of water to stabilize the water environment.

Le Hang

(Agricultural Extension Center)