How to Raise pH in Saltwater Aquarium: Causes and Solutions

pH is a measure of how acidic or basic the water in your saltwater aquarium is. It is important to maintain a stable and optimal pH level for the health and growth of your fish and corals. In this article, we will explain what causes low pH in saltwater aquariums, how to test and monitor pH, and how to raise pH safely and effectively.

how to raise ph in saltwater aquarium

What Causes Low pH in Saltwater Aquariums?

The pH of seawater is around 8.1 to 8.3, which is slightly alkaline. However, in a closed system like a saltwater aquarium, various factors can lower the pH over time. Some of the common causes of low pH are:

  • Low alkalinity: Alkalinity is the ability of water to buffer or neutralize acids. It is mainly composed of bicarbonate and carbonate ions, which are essential for coral calcification and biological processes. Alkalinity is consumed by corals, algae, and bacteria, and can also be depleted by organic acids, carbon dioxide, and nitrate. Low alkalinity can cause pH to drop and become unstable.
  • High carbon dioxide: Carbon dioxide (CO2) is produced by the respiration of fish, corals, and other organisms, as well as by the decomposition of organic matter. CO2 dissolves in water and forms carbonic acid, which lowers the pH. High CO2 levels can result from poor gas exchange, insufficient aeration, or high organic load.
  • Low oxygen: Oxygen (O2) is essential for the respiration of aerobic organisms and the oxidation of ammonia and nitrite. Oxygen levels can decrease due to overstocking, overfeeding, inadequate filtration, or lack of water movement. Low oxygen can cause pH to drop and stress the inhabitants of the aquarium.
  • Other factors: Some other factors that can affect pH are temperature, salinity, substrate, additives, medications, and tap water. For example, high temperature can lower the solubility of oxygen and increase the solubility of carbon dioxide, which can lower the pH. Tap water can contain chlorine, chloramine, phosphate, nitrate, or metals, which can alter the pH and harm the aquarium.

How to Test and Monitor pH in Saltwater Aquariums?

To test and monitor pH in saltwater aquariums, you will need a reliable pH test kit or a digital pH meter. A test kit usually consists of a colorimetric indicator that changes color depending on the pH level. A digital meter uses an electrode that measures the voltage difference between the sample and a reference solution.

To use a test kit, you will need to collect a small sample of water from your aquarium and add a few drops of the indicator solution. Then you will compare the color of the sample with a color chart that shows the corresponding pH values. To use a digital meter, you will need to calibrate it with standard solutions of known pH values before inserting it into your aquarium water.

The best time to test pH is before turning on the lights in the morning or after turning them off at night. This is because pH fluctuates during the day due to photosynthesis and respiration. You should test your pH at least once a week or more often if you notice any signs of low pH such as coral bleaching, fish gasping, or algae growth.

How to Raise pH in Saltwater Aquariums?

If you find that your pH is too low (below 7.8), you will need to take some steps to raise it back to the optimal range (around 8.1 to 8.3). However, you should not make drastic changes or raise it too quickly, as this can shock your fish and corals. Here are some safe and effective methods to raise pH in saltwater aquariums:

  • Increase alkalinity: Increasing alkalinity will help buffer the acids that lower the pH and stabilize it at a higher level. You can increase alkalinity by adding sodium bicarbonate (baking soda), sodium carbonate (soda ash), or a commercial alkalinity supplement. You should follow the instructions on the product label or use an online calculator to determine the correct dosage for your tank size and current alkalinity level.
  • Reduce carbon dioxide: Reducing carbon dioxide will help decrease the amount of carbonic acid that lowers the pH. You can reduce carbon dioxide by improving gas exchange, increasing aeration, or using a CO2 scrubber. Gas exchange occurs at the surface of the water where oxygen enters and carbon dioxide escapes. You can improve gas exchange by increasing water movement with pumps, powerheads, or wavemakers. Aeration involves adding air bubbles to the water with an air pump or a skimmer. A CO2 scrubber is a device that filters out carbon dioxide from the air before it enters the tank.
  • Increase oxygen: Increasing oxygen will help boost the respiration of aerobic organisms and the oxidation of ammonia and nitrite. You can increase oxygen by improving gas exchange, increasing aeration, or using an oxygen reactor. An oxygen reactor is a device that injects pure oxygen into the water with a diffuser or a venturi.
  • Use calcium and alkalinity supplements that are known to raise pH: Some calcium and alkalinity supplements are made from soda ash or kalkwasser (calcium hydroxide), which are known to raise pH. These supplements also provide calcium and magnesium, which are important for coral growth and health. You should follow the instructions on the product label or use an online calculator to determine the correct dosage for your tank size and current calcium and alkalinity levels.
  • Perform regular water changes: Performing regular water changes will help remove excess organic matter, nutrients, and acids that lower the pH. It will also replenish the trace elements and minerals that are essential for the aquarium. You should perform water changes at least once a month or more often if you have a high bioload. You should use RO/DI (reverse osmosis/deionized) water or distilled water mixed with high-quality marine salt to make your saltwater. You should also match the temperature, salinity, and pH of the new water with the old water before adding it to the tank.


pH is a crucial parameter that affects the health and growth of your fish and corals in a saltwater aquarium. Low pH can cause stress, disease, and death in your aquarium inhabitants. To prevent low pH, you should test and monitor it regularly and take steps to raise it if it falls below the optimal range. By following the methods described in this article, you can raise pH safely and effectively in your saltwater aquarium.