A Guide to Clear Aquarium Water

Posted by
Cameron Wise on September 22, 2023

Maintaining a fish tank is much like caring for a plant – a small mistake can yield many negative consequences. Miniscule changes in a fish tank’s chemistry can completely alter the look and health of an aquarium’s water. Much like humans are sensitive to air pollution, fish are susceptible to unwanted pollutants in water. Because of their effects on fish and plant health, contaminants must be reduced in an aquarium. Not only will the fish benefit, but you will also enjoy the sight of a crystal-clear fish tank. In this article, you can discover a couple major ways to keep your fish tank water clean and resources to help you along the way.

Key takeaways

  • Fill your aquarium with reverse osmosis water.
  • Do not take shortcuts when setting up and cycling your aquarium.
  • Use a quality water filter, air pump, and water pump.
  • Inspect your tank and perform small cleaning tasks every day.
  • Fully clean the tank every one to two weeks.
  • Test your water at least once per month and correct issues.

How to get clear aquarium water

Getting clear aquarium water is all about proper preparation and maintenance. Processes must be followed carefully to set up the water’s chemistry, and additional steps must be taken to maintain proper chemical levels.

Set up the aquarium properly

One of the best ways to ensure clear aquarium water is to set yourself up for success from the beginning. When setting up a fish tank, do not take shortcuts and do not introduce fish or plants before the tank is fully prepared for them. To properly set up your aquarium, ensure you follow the steps below. If you have already set up your aquarium and notice you are missing one of these elements, incorporate changes slowly unless your tank is experiencing an emergency. Major, quick changes to a fish tank can disrupt your fish and cause unwanted side effects.

1.  Use reverse osmosis water

When filling your aquarium with water, you want to ensure that the water’s chemistry is ideal for the fish or plant life in the tank. The best way to tailor the water for your tank is to start with a pure foundation. Reverse osmosis (RO) water is free from contaminants, such as nitrates, phosphates, silicates, and water hardness, that are particularly harmful to fish. As a result, it is an excellent type of water to use as a base for your aquarium. Once the tank is filled, you can supply the necessary additives to the RO water. This ensures that the exact levels of each chemical and mineral are ideal for the life in your tank.

Learn more: Why you should use reverse osmosis water for your aquarium

2.  Cycle the aquarium properly

The most important phase of aquarium setup is cycling the tank. During tank cycling, you allow the aquarium to complete what is called the nitrogen cycle. This process converts ammonia to nitrite, nitrite to nitrate, and nitrate to nitrogen gas. Nitrifying bacteria, the catalyst for these conversions, builds up on biofilter media to deal with fish waste, extra food, and other sources of contamination in the tank. Without proper cycling, there will not be enough nitrifying bacteria in the tank to feed on the ammonia produced by the fish, leading to toxic levels of ammonia in the tank.

The cycling process takes time, and some aquarium owners may try to skip certain parts of the process. However, cycling a fish tank is critical in maintaining the future health of the fish and plants inside. The entire process takes between four and eight weeks, and it should be sped up only when necessary.

Learn more: How to cycle a fish tank

3.  Use quality aquarium filtration

Water filtration removes particles, chemicals, and other contaminants that can make aquarium water discolored, cloudy, and unhealthy for marine life. There are three types of aquarium filters: biological, mechanical, and chemical.

Biological aquarium filters

Biological aquarium filters are the most essential type of filter you can have in your aquarium. In fact, it is the only filter that all aquariums must utilize. Biological filters, also known as biofilters, contain pores that house nitrifying bacteria. As water passes through a biofilter, ammonia converts to nitrite, nitrate, and eventually nitrogen gas.

Mechanical aquarium filters

A mechanical aquarium filter is essentially a strainer that catches particulate matter as water passes through. Excess fish food, debris, dirt, and other particulate matter are filtered out through a mechanical filter. While mechanical filters are not essential in removing ammonia, they can prevent source of ammonia from lingering in the water. As a result, they provide excellent assistance to biological filters in any aquarium.

Chemical aquarium filters

Chemical aquarium filters utilize an activated carbon core or some type of resin to remove specific contaminants from water. Chemical filters are more specialized than other filter types, so they are not as universally essential as biological and mechanical filters. Chemical filters remove heavy metals, salt, medication, tannins, and other contaminants from aquarium water.

Because they are specialized, chemical filters are not necessary on a healthy tank. Rather, they are most often used to clear out excess medication from water once it is no longer needed. They can also remove dissolved particles that are not able to be strained out by mechanical filters.

4. Use a water pump

Aquarium water pumps are essential in maintaining water circulation in a fish tank. They ensure all water in the tank flows through the appropriate filters, and they evenly distribute nutrients throughout the aquarium. Aquarium water pumps are not essential in very small-scale aquariums, but they can be beneficial if you notice symptoms of low circulation in your tank, such as the presence of algae in the tank or sluggishness in your fish.

Learn more: What is an aquarium water pump and how does it work?

5. Use an air pump

Aquarium air pumps provide oxygen to a fish tank through airline tubing. While air pumps ensure fish have enough oxygen, they also assist in the filtration of contaminants in the water. At the top of a tank, oxygen enters and carbon dioxide exits the tank via surface agitation. Aquarium air pumps increase the agitation within the tank, allowing more oxygen in and expelling more carbon dioxide. This agitation also increases circulation within the tank, allowing more water to pass through the filters.

Learn more: What is an aquarium air pump and is it necessary?

Follow a maintenance schedule

In both freshwater and saltwater tanks, regular maintenance is key to the overall success of your aquarium. This includes regular chemical testing, cleaning the tank, and performing other maintenance tasks as needed.

Perform daily maintenance tasks

Daily aquarium maintenance tasks ensure that no major changes took place in the aquarium overnight. If checked daily, problems in your aquarium can be resolved before they have a devastating impact on your plants and fish. You should perform these tasks every day:

  • Inspect all pumps, filters, and lights
  • Observe your fish for signs of negative health
  • Top off the tank with filtered water (preferably reverse osmosis)
  • Remove excess food from the tank
  • Ensure the water’s temperature is suitable for your marine life.

Clean your tank every one to two weeks

Cleaning your fish tank prevents hazardous chemicals, grime, or other contaminants from building up in your aquarium. The cleaning process involves unplugging and cleaning all filters, pumps, and lights, removing up to 25% of the tank’s water, scrubbing the inside of the tank, and vacuuming the substrate. If cleaning your tank every other week results in the water becoming cloudy before your next clean, consider increasing the cleaning frequency.

Learn more: How to clean a fish tank

Test your aquarium’s water at least once each month

At least once every month, you should perform thorough testing of your fish tank’s water. Ammonia, nitrite, nitrate, phosphate, water hardness, and pH should all be tested each month. You can easily test aquarium water with test strips. Some test strip kits are designed to test for multiple contaminants at once, while others specialize in a specific contaminant. Specialized test strips will generally be more accurate, but all-in-one test strips are still acceptable to use for aquariums.

If you notice something wrong with the chemical levels in your water, you should follow this guide promptly to correct any issues. While correcting chemical levels, remember that drastic changes can negatively affect fish health. Introduce changes slowly, and never change out more than 25% of your tank’s water at a time.

Learn more: How to maintain a freshwater aquarium | How to maintain a saltwater aquarium

aquarium TDS testing

Frequently asked questions

What makes aquarium water cloudy?

Cloudiness in aquarium water is most often caused by bacterial bloom, algae, or poor water quality. Bacterial bloom occurs when many bacterial colonies appear at once, overwhelming the tank. Both bacterial bloom and algae can be prevented by regular water changes. Poor water quality, on the other hand, requires deeper probing into the problem and solution. The water must first be tested to discover which contaminants are too high or too low for the tank to function properly. Once you know which contaminant must be removed, you can problem solve your tank’s problems.

Can I use tap water for my aquarium?

Tap water should never be used in an aquarium without first being filtered. Chlorine and chloramine, both used to treat bacteria in municipal water supplies, are toxic to fish. Some aquarium owners may fill their tank with tap water and allow it to sit for a few days. While tap water dechlorinates after sitting stagnant for a few days, other minerals, such as water hardness, can negatively affect fish health. For the best results, always use filtered water, preferably reverse osmosis, to fill your aquarium.

When can I add fish to my aquarium?

Fish should not be added to an aquarium until the nitrogen cycle has completed. At this stage, ammonia and nitrite levels should not be detectable during your water tests. If you add fish before the nitrogen cycle completes, your fish will be exposed to toxic ammonia and nitrite.

How many fish can I add to my aquarium?

For small aquariums, a common rule is to never exceed 1 inch of fish for every 1 gallon of water in the tank. However, since some fish are bulkier than others, you must take into account the species of fish being added. If the fish you are using have wide bodies, you may not want to add more than 1 inch of fish for every 3 gallons of water. You will also want to factor the aggression levels of the species of fish you are adding. Territorial fish, for example, may require more or less water or decorations in the tank. Adding too many fish to an aquarium can contribute to cloudy, unhealthy water.

When adding fish to a tank, particularly a new tank, take care not to add too many at a time. This can overwhelm the good bacteria in the tank, not allowing them to manage the ammonia and nitrite created by the large volume of fish. Start by adding only a few fish and slowly introduce more after a few days. It is always better to understock an aquarium than to overwhelm the tank’s ecosystem.


If you have any additional questions about water filtration, please do not hesitate to contact us.

No comments yet.
Leave a comment