pH management of water in aquaculture

In aquaculture, changes in pH can affect physical elements, chemistry, and biology of water environment and health of the species.

Appropriate pH for water in shrimp ponds is pH = 7.2 to 8.8. The best condition is from 7.8 to 8.5.

pH fluctuation during a day should not exceed 0.5. If pH changes significantly, it can make shrimp and fish shocked, weakened and stop eating.

If high or low pH extends for a long time, it will make shrimp grow slowly, stunting and susceptible to diseases.

pH of water depends on these factors:

1. Natural ground/platform of the ponds:

• Acid sulfate soil (acidic alum soil, acidic soil) makes ​​pH of water low and fluctuated. 

• If it rains a lot; aluminum is washed away from dikes into ponds; water soaking in dikes or water in trench leaking to ponds will increase the amount of aluminum in ponds and reduce pH. 

• If we plow the alum ground, aluminum will ​​blow up into the upper floors. 

2. Algae and microorganisms in lakes: 

• Algae and microorganisms using CO2 can affect the pH of water. 

• A large amount of algae will make pH strongly fluctuated during the day. Too much algae also makes pH high (8.8 to 9.1) in the afternoon. 

• When algae dies, pH in ponds will be reduce. 

• In shrimp areas whose salinity is low, or in rainy season, algae often increase. 

• Balance between algae and microorganisms need to be maintained to stabilize pH. 

pH in ponds often increases during the day and decreases at night. It is necessary to measure pH at least 2 times/day to monitor, identify causes of fluctuations and timely control situations.

Some simple solutions that can stabilize pH of water in aquaculture ponds:

1. Handling bottom environment of the ponds:

Using quicklime or slaked lime to renovate ponds’ bottoms.

Check pH of the bottom soil. The lower the pH, the more we have used lime to increase pH. 

• pH > 6: use 300 - 600 kg of lime/ha

• pH < 5: use 1500 - 2000 kg of lime/ha. 

2. Water Treatment:

When pH is low: 

• When pH drops too low, use lime, or slaked lime with a dose of 0.5 - 10 kg/1000 m2. Spread lime around the pond, about 10kg/1000m2 before it rains. 

• For pH in the morning is from 7.5 to 7.8, and the difference in the afternoon exceeds 0.3: If the water is pure, use 30 - 50kg dolomite lime/1600 m2 (180-300 kg/ha) in the afternoon continously in 2-3 days. 

• For pH in the morning is from 7.5 to 7.8, and the differences in the afternoon is 0.5: If the water color is normal, use CaCO3 lime of 180-300 kg/ha every afternoon until the pH stop fluctuate too much during the day. 

In case of high pH 

• If pH > 8.3 in the morning: use sugar with a dose of 1-3 kg/1000 m2, or use appropriate probiotics to stimulate the development of microbial decomposition. These microorganisms decompose organic detritus in the pond. CO2 will be produced and pH will be reduced. 

• pH can be reduced by replacing less water. 

• In case of a sudden increase in sunny afternoons, pH > 9.0, use formalin with a dose of 3-4 ml/m3. 

If pH fluctuation is large during the day (> 0.5), hardness (the amount of CaCO3) in ponds is low, algae grows and develop quickly causing algal blooms, organic detritus increases in ponds, use dolomite lime with a dose of 100-200 kg/ha to increase water hardness and buffering agent. Water should also be changed to stabilize the growth of algae.

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