How to regulate old water that appears in aquaculture ponds?

The "old water" that aquaculture farmers often find is mostly copper-green or dark green, and in more serious cases turns yellow, brown or grayish blue, with thick, turbid water quality, transparency below 20 cm and low dissolved oxygen, so fish tend to gasp at the surface. The water color shows no daily variation, and the number of phytoplankton in the water is large, but most are indigestible species such as blue-green algae. The massive reproduction of phytoplankton causes the pond water pH to be very high, which is unfavorable for fish growth. The following methods are often used for regulation.

1. Clean and prepare the pond

After a year of aquaculture, the bottom of the pond accumulates silt containing large amounts of organic matter and bacteria. Therefore, after each aquaculture cycle ends, dredging and disinfection, etc. are needed to remove harmful substances such as ammonia nitrogen and nitrite, thereby improving water quality.

2. Do not use quicklime

When the water quality of a fish pond is in an old-water state, applying quicklime to improve water quality must be prohibited. This is because quicklime can further raise the pH of the pond water, thereby accelerating the excessive reproduction of blue-green algae.

3. Add and exchange new water

Changing water is an effective way to solve pond water aging. The new water added must have good water quality, be pollution-free and rich in dissolved oxygen. The frequency of adding and exchanging water should be flexibly controlled according to the principles of observing the weather, the water color and the transparency.

4. Turn on the aerator

Use aerators reasonably according to the principle of "three on, two off" to increase dissolved oxygen in the water body, promote material circulation, and transform and decompose harmful substances at the pond bottom.

5. Scientific feeding and application

To reduce the feed conversion ratio of fish and lessen the degree of feed pollution to water quality, compound pellet feed from legitimate manufacturers should be selected. Do not apply organic fertilizer, apply little nitrogen fertilizer, and appropriately increase phosphorus fertilizer according to the pond water quality conditions.

6. Transplant aquatic plants

Transplanting aquatic plants such as water hyacinth and alligator weed into fish ponds can reduce harmful substances such as ammonia nitrogen in the water, and can also absorb nitrogen and phosphorus in the water, dilute the fertility of the pond water and improve the pond water quality.

7. Apply water quality improvers or microecological preparations

For ponds with poor water source conditions or difficulty in adding and exchanging water, water quality improvers or microecological preparations, etc. should be applied regularly during the aquaculture process, which can increase dissolved oxygen at the pond bottom, degrade harmful substances and improve the water environment.

8. Stock filter-feeding fish together

Releasing an appropriate amount of filter-feeding silver carp, bighead carp and allogynogenetic crucian carp, etc. can effectively control the excessively rapid growth of phytoplankton such as blue-green algae and reduce the content of organic debris in the pond.