How to Reduce Turbidity in Pond Water (Best Methods)


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How to Reduce Turbidity in Pond Water

Turbid pond with floating leaves
Suspended fine particles in a pond can cause the water to look murky & make it impossible to see the pond bottom. Photo from PublicDomainPictures.net

Pond turbidity is a common issue in both ornamental and aquaculture ponds, particularly those with earthen floors. It is often caused by the suspension of fine particles, such as those that make up clay soil, in low-alkalinity pond systems. The particles are so lightweight that they remain suspended in the water column and are unable to weigh one another down. They give the pond a muddy or murky appearance, preventing onlookers from seeing the pond bottom or any pond fish.

While this is mostly an aesthetic issue in natural or aquacultural ponds, it can be associated with a number of drawbacks. Ornamental ponds, which tend to house valuable fish species, should ideally be near-crystal clear to be fully appreciated. High water clarity is also associated with a healthy ecosystem, not to mention it places less pressure on the pond filter.

In some cases, excessively turbid pond water can be caused by imbalances in water chemistry, such as an influx of nutrients that induce heavy algal and weed growth. This article will take you through a handful of techniques to help you regain water clarity and maintain it. A thriving pond system that takes the bulk of its energy from sunlight requires clear water. When determining the proper treatment for turbidity, it is necessary to first pinpoint its type and causes.


Types of Pond Turbidity

1) Mineral turbidity

Turbid orange-brown water
Mineral turbidity is common in new ponds and can be recognised by the pond water turning reddish to light brown. Doug Beckers / CC BY-SA 2.0

This type of turbidity is often caused by the suspension of negatively-charged, inorganic particles, such as those that make up compact substrates. Mechanical disturbance of silt or clay soil, which can be caused by rainfall, wave movement, pond aerators, a heavy current, or nuisance fish stirring up the bond bottom, causes the surface particles to become dislodged and float in the water column.

As a result, the pond water turns reddish to light brown depending on the color profile of the bottom and pond edge substrates. The suspended particles may appear to be stationary rather than motile, even in the presence of a current.

Common in new ponds, mineral turbidity may occur due to a lack of vegetation to keep the substrate intact. As more aquatic vegetation colonizes the surface of pond substrates, turbidity levels should become reduced. In fully established or mature ponds, a sudden increase in turbidity can usually be attributed to a single cause. Try to take note of any recent changes or additions to the pond that may have disturbed the sediment. The culprit could simply be a new aerator or a particularly heavy spell of winds and rain.


2) Humic & waste turbidity

Fish food floating on water surface
Uneaten fish food can increase humic turbidity in a pond. shellac / CC BY 2.0

Characterized by the suspension of dark-colored particles, humic turbidity is caused by disturbances to the humus component of the substrate. Humus refers to the organic portion of the soil. It can be composed of dead plant and animal materials that are undergoing decomposition. When suspended, these can cause the pond to have an unappealing odor.

Though humic particles are usually introduced through the water supply, they can be a result of organic materials entering the pond through the surface or the breakdown of biotic components from within the pond itself. In new ponds, with limited bacterial populations, decomposition rates may initially be very slow. Waste buildup occurs as a result. Even uneaten fish food, fecal matter of rapidly growing fish, and seasonal plant decay can increase turbidity rates. As these are often implicated in oxygen depletion and nutrient imbalances, such as the increase of ammonia and nitrites, suspended waste particles can adversely affect fish populations.


3) Plankton turbidity

Thick algal bloom in a pond
Algal blooms can increase turbidity rates up to 40%, starving bottom decomposers and vegetation of oxygen and sunlight. eutrophication&hypoxia / CC BY 2.0

A high concentration of suspended microscopic organisms can alter the clarity and color of water. Depending on the dominant species profile, turbid water can be green, brown, blue-green, or even yellow. While some microbes may be harmful to pond ecology, green-colored species that typically occur in natural ponds should generally be manageable and harmless in controlled concentrations.

Plankton turbidity often occurs in ponds that are fully exposed to sunlight and devoid of floating plants. While mechanical turbidity may adversely affect plankton growth, clear water can encourage it. The high light levels throughout the water column can cause it to become markedly productive.

Productivity is increased even further in high nutrient conditions. An algal bloom can increase turbidity rates to more than 40%, preventing light from reaching the pond bottom. This way, the algae directly compete with pond vegetation for sunlight and oxygen. An unfavorable domino effect, resulting in mass die-offs, can occur as bottom decomposers and vegetation are starved of these resources.


Techniques to Reduce Pond Turbidity

1) Pond filtration

Pond pump underwater
A mechanical pump can help to keep the water clear in ornamental ponds, though it may not be sufficient if turbidity levels are abnormally high. Crinklecrankle.com / CC BY 2.0

A heavy-duty filter can be an effective means of removing considerable amounts of particulate matter from pond water. It must have the appropriate specifications relative to the size of the pond, as a filter that is too small will rapidly become clogged up. Aquaculture systems often make use of a series of sleeve or drum filters, though these can be damaged by heavily turbid water.

In ornamental ponds, a mechanical pump with a filter box can help keep the water clear, but it should not be relied upon as the primary means of particle removal when turbidity levels are abnormally high. If filtration pads or screens are quickly blocked off by filtered inorganic material, bacteria, and algae, the pump may be rendered ineffective. A heavy water change or the use of coagulants may be required to significantly reduce turbidity levels in this case.


2) Use of chemical additives

A murky pond
Chemical treatment should be considered when mineral turbidity levels are exceedingly high. Options include limestone, gypsum, Epsom salts, and alum. Inga Munsinger Cotton / CC BY 2.0

When mineral turbidity levels are exceedingly high, it may be necessary to consider chemical treatment. The compounds listed below are often used in aquaculture ponds to weigh down clay particles and force them to settle. While some are neutral in terms of pH, others can cause harmful shifts when used in faulty doses.

Coagulants can be used to bring down turbidity in large ornamental ponds, but you will have to thoroughly evaluate your pond’s water chemistry to determine the appropriate amendment. Moreover, the volume and pond shape factor into the application method. It may be necessary to test these additives, using your pond water, in a controlled setting. They should only be applied once the cause of turbidity has been correctly identified and addressed.

Limestone (Calcium carbonate)

The least expensive and most readily available among the additives, limestone is a cost-effective means of reducing pond turbidity. It is unfortunately not very soluble in water, which is why it will have to be mixed into a slurry of water prior to being applied, preferably as a spray, onto the surface. Liming can be used to reduce plankton turbidity.

It may not be the best choice for mechanical turbidity as it sinks to the pond bottom and can quickly become covered by settling particles. Multiple re-applications, which can potentially cause shifts in the water chemistry, may be required. If your pond’s pH is above 7.0 and the alkalinity is higher than 50 ppm, consider using a neutral product instead.

Gypsum (Calcium sulfate)

Gypsum is a neutral salt with a higher capacity for dissolution compared to lime. This mined material is frequently used as a fertilizer and as a major component of chalk and plaster. Large amounts may be required to effectively reduce turbidity. Fortunately, as it is neutral, it does not alter water pH.

Gypsum has the capacity to bond with soil particles, preventing them from becoming re-suspended once they have settled. It continuously causes clay particles to become attracted to one another and form clumps, called floccules. Once the floccules are heavy enough, they sink to the pond bottom. This renders it effective as a means to reduce mechanical turbidity. Note that it would be ineffective in hard-water ponds with high calcium hardness levels.

Epsom salts (Magnesium sulfate)

This chemical compound is similar to gypsum, but includes magnesium as a base element instead of calcium. It is a naturally occurring salt that is frequently used as an alternative remedy to many health ailments. In ponds, it can be used as a coagulant to induce the settlement of clay particles. It would be a good idea to compare the results of gypsum and Epsom salts to water turbidity prior to extensive application. Your pond water’s hardness could influence the effectiveness of either compound.

Compared to gypsum, Epsom salts have a higher affinity for bonding with clay particles, requiring the use of a smaller quantity to clear up a pond. Nonetheless, it does have drawbacks too. Apart from acidifying water, it is generally less available and more expensive compared to gypsum.

Alum (Aluminum sulfate)

The use of alum is one of the oldest and most effective means of clearing muddy pond water. When neutral salts and lime are ineffective, alum may be more desirable due to its compatibility with a wide range of water profiles. Its application generates sinking floccules of clay particles. A major downside, however, is its capacity to reduce pH levels.

This amendment would be more ideal for ponds with high pH and alkalinity levels. Ground limestone may need to be used in combination with this compound to even out its effect on the water pH. A water test right after alum application is necessary to ensure a balanced chemical profile.


3) Surface application of hay

Hay on the water surface
Hay can be placed on the water surface as a way to reduce turbidity, though it does have quite a few downsides. bobistraveling / CC BY 2.0

Hay or rice straw have been used in fish ponds to reduce turbidity. Hay can induce the settlement of clay particles by producing organic acids. The acids bond with suspended sediments, forming complexes that are heavy enough to sink to the pond bottom.

Unfortunately, there are many downsides to this cost-effective and simple means of clearing water. First, the hay can induce bacterial growth that will rapidly cause oxygen depletion through the water column. Depending on the source, some types can release colored compounds, such as tannins, that can discolor the water. As the quality of hay tends to vary, there are no known standards for general application rates.


4) Culture-beneficial bacteria

Murky green water
Introducing beneficial bacteria to your pond can help regulate algal blooms and prevent the rapid fluctuation of nutrients. ralmonline alm / CC BY 2.0

Beneficial bacteria can help speed up decomposition rates and regulate algal blooms by assimilating excess nutrients. While a bacterial formulation for freshwater ponds does not necessarily prevent increases in mechanical turbidity, it can prevent the rapid fluctuation of nutrients in the event of an influx of particles. Moreover, beneficial strains can serve as a buffer against changes in water pH.

Do avoid introducing beneficial bacteria to ponds that have depleted oxygen levels as they may simply die off before their populations can dominate the water column. They are best introduced to new ponds or those that have settled substrates (after treatment) as they can help balance out the water chemistry and hasten pond maturity. Biological filter media can help nitrifying bacterial colonies multiply until they are numerous enough to purify pond water.


5) Cultivate more aquatic plants

Floating aquatic plants in a pond
Floating aquatic plants help to prevent plankton turbidity because they compete with microbes for sunlight and oxygen. Ben Chun / CC BY-SA 2.0

When rooted into a pond’s margins or its floor, aquatic plants can keep a firm grip on the substrate. This prevents soil particles from easily becoming dislodged whenever they are disturbed by wave action, currents, or nuisance fish. They also cycle excess nutrients in the pond, reducing the likelihood of plankton blooms. Floating plants can likewise prevent plankton turbidity as they compete with microbes in the water column for sunlight and oxygen.

Aquatic plants should be introduced into the pond while the water is clear. Don’t simply place new pots of plants in turbid water and expect them to magically cause the particles to settle. They can rapidly perish in turbid conditions as they require sunlight to survive. Their water-clearing functions take time to play out. Keep in mind that they can only serve as natural filters if their basic requirements for survival are met.


6) Perform a heavy water change

Fish in clear water
Sometimes when trying to reduce pond turbidity the most effective solution is to do a heavy water change. Photo from pxfuel

Sometimes, the only truly effective means of reducing turbidity in a pond is by replacing a considerable portion of the turbid water with fresh, clean water. This only makes sense if you’ve already addressed the root cause of turbidity; it would be costly, time-consuming, and wasteful to constantly replace the water due to repeated instances of sediment suspension. Moreover, when heavy water changes (above 40%) are performed too frequently, beneficial bacterial populations may struggle to recover and your pond fish may become repeatedly stressed.


7) Remove sludge

Sludge in an empty pond
Sludge is found at the bottom of a pond and contains fish waste & other decomposing organic materials. Remy Sharp / CC BY-SA 2.0

Sludge, which contains fish waste and other decomposing organic materials, can settle on the pond bottom and form a mound of toxic compounds. This often occurs in ponds with low oxygen and a lack of natural decomposers. When disturbed, sludge particles can pollute the water column by releasing flumes of particles that are rich in ammonia and sulfur. Sludge can manually be removed with a pond vacuum or with the help of a sludge remover.


Importance of Maintaining a Clear Pond

Koi fish in murky water
Turbid water can prevent fish owners from spotting sickly fish and quarantining them before they spread disease to others. Ivan Radic / CC BY 2.0

Turbid water can be detrimental to the health of your fish and aquatic plants. Just as we are sensitive to heavy air pollution, biotic pond components can struggle to respire in particulate-rich water. Clay and waste particles may become trapped in the gills of fish. They may also prevent visual feeders from finding food.

In natural lakes and ponds, turbidity affects the survival of zooplankton communities. This can spell trouble for predators that are located higher up the food chain as zooplankton are a vital source of nutrients for primary consumers. Phytoplankton and aquatic plants rely on sunlight, which can hardly penetrate through turbid water. Ultimately, dead zones can begin to arise as live organisms become light-deprived and suffocated.

The harmful effects of turbid water don’t stop there. In ornamental ponds, it can prevent pond owners from spotting sickly fish and quarantining them before their diseases can spread. Also, it would complicate the removal of detritus, uneaten fish feeds, and dead animals as the pond bottom can cease to be visible. It’s best to adopt a pro-active rather than reactive stance to pond turbidity as prevention can save you tons of time, money, and effort.

As a rule, conduct routine tests to evaluate the nutrient concentrations, oxygen content, and pH. You may also opt to test for water transparency using a Secchi Disk or submit a water sample to your local laboratory to obtain TSS (total suspended solids) value. Ideally, TSS concentrations for ornamental ponds should be kept at a low value (~25 mg/liter or less). For aquaculture ponds, values approaching 100 mg/liter are more acceptable as higher turbidity can prevent predation and weed growth.

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