Why is my fish tank cloudy after water change? 

Fish tanks (aquariums) are greatly increasing in household scenery around the continents. Keeping these fish tanks has become more of a habit in the new world. This article will cover the concern “Why is my fish tank cloudy after water change?”, reasons behind it, etc. 

Why is my fish tank cloudy after water change? 

Fish tanks appear cloudy after water change because the minerals and nutrients in water support the growth of bacteria. Water change in a tank cleans water temporarily, but after two to three days, cloudiness reappears because of the bacterial bloom. 

Water containing excess organic matter can also support the growth of bacteria and can cause cloudiness. Other reasons may be that aquarium gravel was not cleaned properly, dust accumulating in the tank, or excessive sediment or minerals in the aquarium water. 

Causes of cloudiness in fish tanks 

The following are the possible causes of cloudiness in fish tanks: 

Green water 

Green water is because of the algae growth. It’s difficult to get rid of it, but once you know the cause, it can be cured. The following are the primary causes of green water: 

  • Too much sunlight or leaving the lights on for too long will promote algae growth. 
  • Excess nutrients promote algae growth and must be reduced to battle algae. It’s important to remove nutrient sources to avoid green water. 
  • Phosphates come from decaying matter and from the water itself. Testing your water for phosphates and using phosphate remover to treat the water is recommended. 
  • Nitrates usually rise in water as a byproduct of fish waste. The only possible way to remove it is by changing the water. 

Immediately after setup 

If your tank starts showing cloudiness immediately after tank setup, it’s because the aquarium gravel may not have been rinsed properly and dust from the gravel has made its way into the tank. 

Bacterial bloom 

If a cloudy water tank occurs a couple of weeks after a tank is started, then the reason behind it is the bacterial bloom because of the buildup of organic matter in the water. Cloudy aquarium at this stage is often regarded as “New Tank Syndrome”. 

After a partial water change 

If the cloudy aquarium water appears after the initial water fill or after a partial water change, then the issue may be from heavy sediments or minerals in tap water. 

After a tank cleaning 

If a tank shows cloudiness after tank cleaning, after a filter cleaning, or after stirring up aquarium gravel, then it’s the result of an excessive release of organic materials into the water column. 

The key to correcting cloudy aquarium water is figuring out exactly when the cloudiness started. Dealing with these issues smartly, methodically, and patiently is suggested. When cloudiness appears, aquarium hobbyists  should take notice of it and think of a solution. 

Role of fish waste and heterotrophic bacteria in causing cloudiness 

A cloudy aquarium is mostly the result of a bacterial bloom occurring because of excessive dissolved organic materials in the water column. Organic material in freshwater comes from fish waste or excrement, uneaten fish food, dead plants, dead fish, dead snails, or other debris. 

Heterotrophic bacteria 

The rapid population growth because of feeding on high levels of organic materials dissolved in the water column supports the growth of heterotrophic bacteria. This sudden bacterial growth is known as bacterial bloom causing white cloudy aquarium water. 

Bacteria consume large amounts of oxygen in aquarium water, so after the onset of bacterial bloom make sure the aquarium gets additional aeration. Bacterial bloom may also be involved in raising ammonia levels, so make sure to check for Ammonia spikes.

Organic materials 

Changing aquarium water with dechlorinated tap water may temporarily clear the tank, but unless the levels of organic materials are reduced, the problem will keep coming again and again. Within a few hours, the new water in the tank will be cloudy again. 

How to remove cloudiness in fish tanks? 

The best way to treat cloudy aquarium water is removing excessive organic materials that are causing bacterial bloom. First remove uneaten fish food, dead fish, dead snails or dying aquarium plants. Then carefully swish out the aquarium filter with tank water and then rinse out the aquarium filter media. 

The decision when to remove waste from the bottom of the tank can play a key role in removing cloudiness from aquariums. A net can be used to scoop out the floating debris and waste laying on top of the gravel. You can also create current to remove heavier debris. 

Make sure not to accidentally release more fish waste back into the tank while cleaning. Take care not to damage or destroy the anaerobic nitrifying bacteria in the filter box or filter media. Disturbing an aquarium’s biological filter may cause a mini-cycle or full blown aquarium cycle. 


Today, we covered the article “Why is my fish tank cloudy after water change?”, reasons behind it, etc. From the above discussion it’s clear that fish water tanks appear cloudy because of the organic material buildup in it that supports bacterial bloom. 



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