How to Maintain a Saltwater Aquarium

Posted by
Cameron Wise on April 24, 2023

Maintaining a thriving saltwater aquarium may seem like a daunting task, especially when compared to its freshwater counterpart. However, with the right knowledge and commitment, even beginners can master the art of saltwater aquarium care. In reality, the process is quite similar to caring for a freshwater tank, with just a few additional steps to keep your vibrant marine life healthy and happy. Dive into the world of saltwater tank maintenance with this comprehensive guide, covering everything from daily tasks to essential chemical adjustments. Learn the secrets to creating a captivating underwater oasis for your fish and plants, and unlock the beauty of the marine world right in your own home.

Saltwater maintenance tasks

Certain saltwater aquarium maintenance tasks must be performed daily, weekly, or as needed. The frequency certain tasks must be performed may change as the tank matures.

Daily saltwater tank maintenance

Alongside feeding your fish, several tasks must be completed daily to maintain the health of your saltwater aquarium.

1.   Inspect the tank.

A tank’s water, fish, plants, and accessories should be checked daily for signs of disease, wear, color changes, or changes in behavior. Ensure that all items in the tank are accounted for and that no major disturbances have taken place. Feeding time is an optimal window to inspect all your fish and observe any behavioral changes.

2.   Check water temperature.

Water temperature must remain consistent to prevent illness in fish, especially in saltwater aquariums. For reliable measurements, use a submerged or digital thermometer, not an external one. The temperature inside a saltwater aquarium can range from 73 to 84 degrees Fahrenheit, but the ideal temperature for your tank depends on the fish and plant life inside. Once an acceptable temperature is reached, maintaining a consistent temperature inside a saltwater aquarium is crucial in preventing illnesses in fish and diseases in plants.

aquarium thermometer

3.  Top off the tank’s water.

Water evaporates from a tank on a regular basis, meaning this vaporized water must be replaced. Keep in mind that water evaporates, but the salt inside the tank does not. Because of this, only freshwater should be used to top off the water in a saltwater tank. When topping off your tank, use reverse osmosis water to provide the purest water possible for your aquatic life.

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

Weekly and bi-weekly saltwater tank maintenance

When planning an aquarium maintenance schedule, set aside a consistent weekly time to perform these important maintenance tasks.

1.   Check water quality.

Once each week, you should check the salinity, specific gravity, pH, alkalinity, ammonia, nitrite, and nitrate levels of the water in your tank. The appropriate levels for these elements are the following:

  • Fish tank salinity – 34-36 ppt (parts per thousand).
  • Reef tank salinity – 32-33 ppt. Certain corals cannot tolerate the same salinity levels that saltwater fish can. In a reef tank, salt levels should be kept slightly lower than in fish-only tanks.
  • Specific gravity – 1.020 – 1.026. The specific gravity of a liquid is its density relative to the density of pure water. Because saltwater contains more contaminants than freshwater, the specific gravity of saltwater is naturally higher. Specific gravity is relative to salinity, so the specific gravity of a tank should be in range if the salinity is also in the appropriate range. The specific gravity of ocean water is about 1.026, so a saltwater aquarium should hold a specific gravity close to this number. Reef tanks should maintain a specific gravity on the lower end of this range because corals cannot withstand the same salinity that fish can.
  • pH – 8.0-8.4. The pH of saltwater is higher than that of freshwater because of the carbonate concentration, also called alkalinity, of saltwater.
  • Alkalinity – 8-12 dkh (degrees of carbonate hardness). The alkalinity of water often correlates to its pH. If your water’s pH is low, raising its alkalinity is an excellent way to raise both levels.
  • Ammonia – Close to 0 ppm (parts per million). Ammonia enters a tank through fish waste and old food particles. It is extremely harmful to fish, which is why it must be broken down for the tank to thrive. While fish constantly fill an aquarium with ammonia, the biological filters in a tank convert it into nitrite and, subsequently, nitrate. In a healthy tank, ammonia levels should remain as close to zero as possible.
  • Nitrite – Close to 0 ppm. In the nitrogen cycle, ammonia converts to nitrite, which then converts to nitrate. Like ammonia, nitrite levels should be as close to zero as possible in a properly cycled aquarium.
  • Nitrate – 0 – 40 ppm. Nitrate, a safer form of nitrite, is the final product of conversion in the nitrogen cycle. Nitrite converts when nitrifying bacteria in the tank break this nitrite down into nitrate. Saltwater fish and plants can often tolerate nitrate levels as high as 40 ppm, but nitrate levels should still be kept as low as possible.

Learn more: How to cycle a fish tank

2.   Perform a water change.

At the beginning of your aquarium’s life, between 10 and 25 percent of the tank’s water should be replaced each week. As the tank matures, you may be able to change the water once every two weeks. If you perform water changes bi-weekly and begin to notice problems in your tank, revert to changing the water once per week. Regular water changes prevent pH changes, ammonia spikes, and cloudy water. Do not change more than 25 percent of a tank’s water at a time. Too much change in a tank’s ecosystem can shock fish, increasing the chances of illness and disease. Likewise, changing less than 10 percent of a tank’s water at a time does not rid the tank of enough contaminants.

3.  Scrub the tank’s walls

Algae can become a serious problem in an aquarium, particularly if there is an abundance of plant life. A magnetic scrubber allows you to clean both the inside and outside walls of the tank at the same time. Depending on the life inside your tank, the walls may only need to be scrubbed monthly, while other tanks must be scrubbed at least once per week. If your algae problem is severe, you need to increase the frequency of your water changes.

aquarium magnetic scrubber

4.  Inspect filter media and pumps

Each week, you should ensure each filter and pump is operating correctly. If a filter is clogged, it must be either replaced or cleaned. Keeping a replacement filter on hand at all times is a good idea for new aquarium owners who are unfamiliar with how long their specific filter typically lasts in their tank. If a pump seems to be failing, ensure the tubes are not clogged, disconnected, or cracked. You should also check the power source for any sources of electrical-related problems.

As-needed saltwater tank maintenance

Making additional saltwater solution is a task that does not require a specific timeline. While saltwater should be added at regular intervals, it should be made well ahead of time.

1.  Make a saltwater solution

When your aquarium’s salinity drops too low due to salt creep, you will need to add saltwater to the tank. You will also need to prepare a saltwater solution for each water change. In a standard water change, you should add the same concentration of salt to your solution as is already in the tank. This will ensure that the water’s salinity remains constant. If your salinity is too low, you can add an appropriate amount of salt to the water you top the tank off with. When introducing extra salt to the tank, do so slowly and ensure that the water being added to the aquarium is the same temperature as what is already inside.

Some saltwater solution to add to a tank should be available at all times. Once a solution is made, it must be allowed time to warm and aerate before it can be added to a tank. Ensure you make enough saltwater solution for a water change at least one day in advance.

How to adjust chemical properties in a saltwater tank

If the water in your tank fails to meet the appropriate parameters, you can use the following methods to adjust each chemical property when needed.

How to adjust pH in a saltwater tank

The pH in a saltwater aquarium can be raised in many different ways.

  • Bring in outdoor air. If the indoor air contains too much carbon dioxide, it can cause a tank’s pH to lower. Bringing in air from outside depletes CO2 levels and helps restore pH to a higher level.
  • Use a CO2 scrubber. CO2 scrubbers attach to the air intake of a tank and filter out the CO2 before it can enter. This depletion of carbon dioxide allows the pH of the water to rise to the appropriate level.
  • Check the alkalinity. Too high or too low of alkalinity in a tank can cause plants to perish and pH to fluctuate. If you notice your water’s pH is too low, check the alkalinity before attempting to resolve the pH. Adjusting the alkalinity appropriately may resolve both the problems of bad alkalinity and pH.
  • Use limewater. Limewater, also known as kalkwasser, is a calcium hydroxide solution with a pH of 12.4. To make a solution of kalkwasser, add kalk powder to water you will use to top of your tank. Never add kalk powder directly to your tank. Add ½ teaspoon of kalk powder to one gallon of water. Allow the top-off water to sit for 30 minutes before adding it to your tank. Kalkwasser should be added to your tank slowly. Use a dosing pump or manually drip the solution into the water, ensuring that the pH does not change too quickly. Certain dosing pumps automatically shut off if the pH changes too much too quickly.

The pH in a saltwater aquarium can be lowered by adding small amounts of white vinegar. For each gallon of water in your tank, add one mL of white vinegar to reduce the pH by 0.3. Be careful not to put any more vinegar than necessary, as it can be toxic to fish in high enough concentrations.

aquarium pH test

How to adjust salinity and specific gravity in a saltwater tank

The salinity and specific gravity in a saltwater aquarium are simple and convenient to regulate because they can be adjusted during routine water changes.

If your tank’s salinity and specific gravity are too low, you can increase the salt added during water changes. When mixing the saltwater solution, allow it to sit for at least a few hours before measuring its salinity. This gives the solution time to heat to room temperature and aerate.

You can decrease the salinity and specific gravity of a saltwater tank by incorporating freshwater during water changes. When adding freshwater or saltwater, ensure that the water added to the tank is at the same temperature as the water already inside.

How to adjust alkalinity in a saltwater tank

To raise alkalinity in a saltwater aquarium, use a solution of sodium bicarbonate and water. Add 2 tablespoons of sodium bicarbonate to one gallon of water. Stir or shake the solution until the sodium bicarbonate has completely dissolved. Once the solution is ready, dose it slowly into your tank. During and after the time of dosage, monitor the alkalinity and pH of the water to ensure the changes in both are not drastic.

To lower alkalinity in a saltwater aquarium, simply make water changes more often. If you are performing water changes once every two weeks, for example, begin making changes every week. If you are changing a low percentage of water, such as 10 percent at a time, up the changes to 15 or 20 percent. Using reverse osmosis water will ensure that you are adding water to the tank that is free from alkalinity.

Learn more: What is a reverse osmosis system?

How to lower ammonia levels in a saltwater tank

Ammonia is a toxic byproduct of fish waste and uneaten food. If it is not dealt with, the entire aquarium suffers as a result. To lower ammonia levels in an aquarium, try one of the following solutions:

  • Clean your tank and replace up to 25% of the aquarium’s water (if not already completed). This is the first solution you should attempt.
  • Introduce more air into the tank with an air or water pump.
  • Ensure the tank’s pH is not too high.
  • Add beneficial bacteria to the tank.
  • Improve the tank’s filtration. This may mean installing a new filter or cleaning a clogged one.

Learn more: What is an aquarium air pump? | What is an aquarium water pump?

How to lower nitrite and nitrate levels in an aquarium

Nitrite levels in a tank should be as close to zero as possible, while nitrate levels should be kept under 40 ppm. If your water contains above these levels, attempt the following solutions:

  • Clean your tank and replace up to 25% of the aquarium’s water (if not already completed). This is the first solution you should attempt.
  • Introduce more air into the tank with either an air or water pump.
  • Add beneficial bacteria to the tank.
  • Ensure that you are not overfeeding your fish. Excess food is a common contributor to high nitrate levels. If there is too much food floating in the water, remove the excess immediately.

Learn more about aquarium maintenance: How to maintain a freshwater aquarium


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

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