Cloudy aquarium water can have many causes, but most often it is either put into the aquarium in a turbid state (cloudy), or the water becomes cloudy after some time in the aquarium.

When cloudy water is used to fill an aquarium, the causes for the cloudy water are one of the following:

• Algae
• Sediment
• Organic matter
• Silt
• Clay
• Phytoplankton
• Other pollutants and materials

Often cloudy water has its origins from a well or another water source collecting rainwater.

Well water can often be cloudy due to suspended particulate matter. The suspended particles of matter are often sediment, silt, or clay.  These items are found in abundance in new wells or wells that are drilled too shallow for the aquifer or too deep for the aquifer.

An aquifer is bounded on all sides by a sandy buffer which surrounds the body of water.  When a well head penetrates into the sandy buffer there is often a great deal of particulate matter that is disturbed and surrounds the well head penetration.

To clear this particulate matter it is suggested to run the well pump for a period of time to suck the fine particulates in close proximity to the well head out from the adjoining sandy material.  Often a well will, over time, produce clearer water as the fine particulates are removed from around the well pump area.

Cloudy water can also be caused by organic matter such as algae or other phytoplankton suspended in the water.  This is generally not associated with well water.  Large amounts of organic matter are often found in streams or cisterns where biological products find their way into the water containment areas.

There are all sorts of biological matter than can, in sufficient concentrations, cause water to become cloudy.  Fortunately, removal of particulate matter, biological, mineral, or other is a straightforward process.

Introduction of a micron filter in the water pathway will remove the majority of particulate matter.  Most canister type filtration systems are well able to address this problem.

Clouded water affects plants in two general areas.  Clouded water reduces the ability of light to reach plants and clouded water impedes the ability of the plant to gain access to Oxygen necessary for root respiration.

Light, measured in lumens, is essential for plant photosynthesis.  Without sufficient light all plants cease to produce sugars through photosynthesis and eventually die off.

Water absorbs and scatters light, causing it to diminish in intensity as it goes deeper.

Using the Beer-Lambert Law. The Beer-Lambert Law describes how the absorption of light changes with distance through a medium and is defined as:

Clear ocean water has an absorption coefficient in the range of 0.04 to 0.15 per meter for visible light. For freshwater, the absorption coefficient can be higher, particularly in turbid or algae-rich water.

A typical clouded aquarium may have between 10-20 NTU in turbidity.  The effect on plants in the aquarium is significant in terms of lumen penetration through the water.

Aquarium plants can generally tolerate a loss of 10% lumens as found at the 2 foot depth, as they are often adaptable to varying light conditions. However, the specific impact on a plant depends on its light requirements, the species of the plant, and other factors in the aquarium environment.

Factors to Consider:

• Light Requirements: Different plants have different light requirements, ranging from low to high. Plants that require high light may show signs of stress with a 10% reduction in light, while low-light plants may not be noticeably affected.
• Duration of Reduced Light: If the reduction in light is temporary, most plants will be able to adapt without long-term negative effects. However, prolonged insufficient lighting could lead to stunted growth, reduced vitality, and other issues.
• Compensatory Factors: If other conditions in the aquarium are optimal (such as nutrients, CO₂ levels, and water quality), plants may be able to compensate for a slight reduction in light.
• Acclimation: Plants can acclimate to changes in light levels over time. A gradual reduction in light is less likely to cause stress than a sudden change.

Signs of Insufficient Light:

• Stunted Growth: Plants may show signs of stunted growth or elongated stems as they stretch towards the light source.
• Color Changes: Some plants may lose their vibrant colors, becoming pale or yellowing.
• Leaf Drop: Older leaves may drop off, and new growth may be sparse.

In large home aquariums or in commercial settings where depth may be as much as 10 feet, the loss of light from turbidity can significantly impede the health of aquatic flora.

Assume a hypothetical scenario where an increase in NTU leads to a proportional decrease in dissolved oxygen levels. For example, a 10% increase in NTU might lead to a 1% decrease in O₂ levels, and a 20% increase in NTU might lead to a 2% decrease in O₂ levels.

The red dashed line represents the dissolved oxygen levels in clean water for comparison.​

Turbidity in the aquarium water does have an effect on O2 availability, but not significant enough to be evident in flora demise.  However, O2 availability combined with other factors may introduce sufficient stress to be evident in the vitality of the aquarium flora.