The Harm of Too High or Too Low pH in Aquaculture and Prevention and Control Measures
pH is an important water chemistry indicator in aquaculture, and is an indicator for evaluating the strength of acidity and alkalinity of a water body. Generally, a pH of 6.5-8.0 is regarded as neutral, a pH of 5.0-6.5 as weakly acidic, and a pH of 8.0-9.5 as weakly alkaline. The activities of freshwater aquaculture animals, the reproduction of phytoplankton, changes in water temperature and salinity, alkalinity, hardness, changes in the carbon dioxide balance system in water, and the decomposition efficiency of organic matter in the bottom sediment all affect changes in the pH of the water body. Generally, the pH of pond aquaculture water is preferably 6.5-8.0, neutral to slightly alkaline. When the pH is too low, under acidic conditions the reproduction of beneficial microorganisms is hindered, the mineralization rate of organic matter decreases, and the rate of material metabolism declines, making it difficult for phytoplankton to proliferate in large numbers and making it hard to fertilize the pond water. At the same time, sulfides exist more in the form of hydrogen sulfide molecules, the concentration of metal ions in the water body increases, and the toxicity of heavy metals is strengthened, directly producing toxicity to freshwater aquaculture animals. Moreover, in acidic water bodies, freshwater aquaculture animals have poor blood oxygen-carrying capacity, resulting in hidden surfacing behavior. A pH that is too low is often related to factors such as acidic soil and an excessively small amount of phytoplankton in the water body. When the pH is too high, it indicates strong alkalinity, which affects the dynamic balance of ammonia nitrogen and molecular ammonia, making the concentration of molecular ammonia too high and harming aquatic animals. At the same time, an excessively high pH very easily leads to cyanobacteria blooms. A pH that is too high is often related to factors such as a large amount of phytoplankton consuming carbon dioxide and insufficient alkalinity and hardness of the water body. The 24-hour change in pH in an aquaculture pond generally should not exceed 2, otherwise it indicates that the water body is in an extremely unstable state, which very easily causes the phenomena of "water turnover" and "algae crash", inducing mass death of freshwater aquaculture animals.
[Prevention and Control Measures] When the pH is too low, quicklime is mainly used for whole-pond broadcasting, generally at 15-20 kg per mu per meter each time.
When the pH is too high, there are four methods:
1. Broadcast Houmu Jiedu Jingshui Bao over the whole pond (use 3 mu per meter depth for every 1000 ml) for adjustment;
2. Broadcast Houmu lactic acid bacteria over the whole pond (use 3 mu per meter depth for every 500 g) for adjustment;
3. Broadcast benzalkonium chloride or copper sulfate over the pond to appropriately control algae reproduction;
4. Draw out part of the water from the bottom layer and replace part of it with new water.
