What are the Uses of Dolomite in Aquaculture? (Dolomite Pros & Cons)

The global demand for seafood has highlighted the importance of aquaculture practices, paving the way for the development of efficient strategies to improve and hasten fish growth. Increasingly intensive forms of fish production have led to a need for reliable pond treatment additives, one of which is dolomite.

Essentially a form of lime, dolomite is known in every chemist’s notebook as calcium magnesium carbonate or CaMg(CO₃)₂. It is a vital ingredient for a successful harvest, especially in tropical shrimp or fish farms that make use of fully stocked outdoor pond systems.

In nature, dolomite is seldom found in its pure form as it will often contain trace amounts of natural elements. It is a rock-forming mineral and is an integral component of dolostone, which occurs in large deposits that extend to thousands of meters thick. Dolomite is produced via a process that is aptly termed dolomitization, and is very close in composition to what we commonly refer to as limestone or calcite. In contrast to calcite (CaCO₃, calcium carbonate found in corals and phytoplankton exoskeletons), dolomite is rich in magnesium.

Why is Dolomite Used in Ponds?

In aquaculture, dolomite is used as a pond conditioner. It is known for being one of the least reactive forms of lime, making it a prime candidate for use during the fish culture period. In the form of finely pulverized powder, dolomite can be sprinkled onto water and allowed to sink or dissolve. It can also be used to treat soil prior to filling a pond with water. Oftentimes, this process of using dolomite is referred to as ‘liming’ and is as necessary a procedure to pond maintenance as ensuring that fish have access to oxygen. But why exactly is liming so important, and what happens to aquaculture ponds if this step is overlooked?

Over time, the ecology of aquaculture ponds can be thrown off balance by an ever-increasing biomass. This is a given as the reared animals increase in size, along with planktonic and bacterial communities. As all occupants grow, the pond’s carrying capacity is challenged by an influx of waste materials. This results in pH levels decreasing, vital nutrients being depleted, and the accumulation of potentially toxic waste products. Left unchecked, an intensive pond can crash due to acidic conditions, and an altered nutrient profile can stimulate the growth of harmful biota that thrive in low oxygen levels. When applied at just the right time, and coupled with proper pond aeration, dolomite is oftentimes instrumental in preventing these disastrous events.

Benefits of Dolomite Use in Aquaculture & Ponds

1) Dolomite as a disinfectant

Earthen aquaculture ponds are often pre-treated with dolomite, even prior to being filled with water. Its ability to reduce soil acidity discourages the growth of pathogens and kills off existing parasitic communities. Coupled with UV exposure in outdoor ponds, covering the bottom sediment with a thin layer of dolomite can cause a caustic reaction that is efficient in sterilizing at least the top few inches of soil. This step is vital, as pre-existing pathogens can wreak havoc on pond communities if not eliminated beforehand. Moreover, there are harmful parasites that can exist in their dormant states in soil. Liming soil may also be beneficial at a later point, as dolomite in mud can act as a buffer or alkaline reserve.

2) Dolomite as a pH regulator

Pond water acidity is influenced by a complex combination of factors, such as photosynthesis, carbon dioxide availability, water hardness, and pond aeration. To counter pH fluctuations that will naturally occur as a result of gradual waste accumulation, nutrient decomposition, and CO₂ accumulation in water, a pH buffer must be employed. Dolomite, as a carbonate substance, can improve the buffering capacity of water by increasing its alkalinity. There are guidelines to observe, however, as its liberal use can be potentially harmful to the pond’s occupants and financially detrimental to aquaculture farmers.

Prior to liming a pond, its total alkalinity must first be checked with the appropriate test kit or submitted to a water testing laboratory. If this parameter dips to below 30 mg/L, dolomite application may be considered. Application amounts will vary according to the pond’s soil type, total alkalinity values, and size.

3) Dolomite as an additive to increase macronutrients

Macronutrients inevitably become depleted in outdoor pond set-ups, where pond biota will gradually increase in concentration over time. Decomposition of pond waste may also strip the pond of nutrients and oxygen, and is an unfortunate consequence of intensively stocking ponds. In order to counter macronutrient depletion, dolomite can be used to treat pond water. As it naturally contains trace elements, dolomite application will increase the availability of macronutrients such as calcium, sodium, magnesium, phosphorus, potassium, and chlorine. Moreover, by providing trace amounts of iron, zinc, copper, cobalt, boron, manganese, and copper, it can improve the growth of fish and microbial communities.

4) Dolomite as feedstock for microbiota

A vital benefit from dolomite application, the increase in trace element concentrations encourages the growth of phytoplankton and other aquatic plants. Almost akin to a food supplement for pond microbiota, dolomite can help create a rich pond environment for beneficial algae and bacteria. These microscopic communities are more important than they’re given credit for, and can sometimes be instrumental in maintaining clear pond water and breaking down organic waste. Beneficial communities can even prevent pathogenic attacks and the occurrence of harmful algal blooms, which would otherwise cause a pond system to collapse.

Is Dolomite Harmful to Animals & Humans?

Though its benefits are numerous, dolomite must be administered cautiously. It is associated with a few health hazards in humans, such as respiratory disorders and irritation of the skin and eyes. It is not necessarily considered a carcinogenic substance, but it does contain crystalline silica that can damage lungs under prolonged exposure. Use of a mask and protective clothing when handling this substance is recommended.

Additionally, the haphazard use of dolomite can markedly increase the water pH level to a value that is toxic for fish. If far more than the recommended amounts are added, pond water can also grow turbid, blocking out sunlight that is necessary for the proliferation of beneficial microbiota. As a rule of thumb, proper parametric tests should be performed prior to administering dolomite. The time, method, and frequency of application must likewise be considered so as to maximize benefits.