How to Lower pH in Aquariums

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Achieving the right pH balance in your aquarium is crucial for the well-being of your fish. In this blog post, we will delve into the significance of pH levels and discuss effective methods to lower pH when necessary. Discover the circumstances that may warrant pH adjustment and explore practical solutions for creating a balanced aquatic environment. From diluting with RO water to understanding the acceptable pH range for your fish, we’ll guide you through the essentials of maintaining a healthy pH in your aquarium. Get ready to dive into the fascinating world of pH balance!

Family Handyman Magazine reached out to me recently as they were preparing an article on how to lower pH in the home aquarium, and I wanted to emphasize a few points from my discussion with them.

Reduce alkalinity and the pH Will Follow

Rather than reaching for chemicals, to lower pH more safely and effectively, consider diluting your tap water with Reverse Osmosis filtered (RO) water. RO water has lower mineral content, reducing alkalinity and with pH levels ultimately stabilizing at a lower level.

aquarium pH

Consider pH like a seesaw, with acid on one side and base on the opposite. When the acid outweighs the base, the pH will drop into the acidic range. The term for the amount of base you have in your aquarium is called the Alkalinity or Carbonate Hardness (or KH).

Thus, you can lower pH simply by reducing the amount or “weight” of the base in your aquarium, or more specifically by lowering the alkalinity.

By virtue of the acid created by the nitrogen cycle, your tank will already have some acid.

By blending RO water with your tap water, you can gradually achieve the desired pH. Monitor the pH closely during this process and make adjustments accordingly. Remember to conduct regular water tests (including ammonia, pH, and alkalinity/KH) to maintain a stable and healthy of your aquarium.

Always monitor your fish’s behavior closely for signs of stress. This may include dramatic color shifts, rapid respiration (gills opening and closing quickly), it may also be inactivity near the bottom or top of the tank.

Monitor pH and Ammonia Levels Closely

When lowering the pH in your aquarium, it’s essential to monitor ammonia levels closely, particularly when pH values fall below 6.5. Nitrification slows at a pH of 6.5 and essentially stops below 6. Thus low pH can lead to ammonia spikes, which can be harmful to fish. Use reliable ammonia testing kits to regularly monitor ammonia levels and take immediate action if an increase is detected. Performing partial water changes to manage ammonia levels is the simplest and most effective method of ammonia removal to maintain a safe and healthy environment for your fish. Remember, “the solution to pollution is dilution”. 

Remember, when using tap water always use a water conditioner that detoxifies ammonia.

Acceptable pH Ranges for Tropical Fish

Before embarking on a pH alteration project, perhaps you should stop and ask yourself “Why?”

Tropical fish, often captive bred in tap water, tend to thrive within slightly alkaline pH ranges commonly found in tap water.

Additionally, it may be prudent to prioritize stability over achieving an “ideal” value, as lower pH levels can lead to ammonia spikes that require diligent aquarium water monitoring for a healthy environment. 

Ultimately, aiming for a tank with a stable pH is the best goal to ensure the well-being of your fish, and having a slightly alkaline pH due to an alkalinity value that prevents large pH shifts is the easiest way to achieve this goal.

However, there are situations where a lower pH is more crucial. An example would be if you are trying to raise or breed some of the more specialty species of fish such as some Rasbora, Amazonian cichlids, or peat-loving killifish as just a few examples.

Another situation where a slightly acidic pH is ideal is for densely planted aquariums called Aquascapes. There are a variety of reasons for this to be the case from the bio-availability of micro-nutrients such as potassium or iron to the plant’s preference for ammonium (NH4) which will be the prevalent form of ammonia in an acidic environment.

In the case of a densely planted aquarium, it is best to lower pH using carbon dioxide, which we will leave as a topic for a future blog.


Lowering the pH in your aquarium requires careful consideration and monitoring to create a balanced environment for your fish. Remember to conduct regular water tests, observe your fish’s behavior, and make adjustments gradually to maintain a stable pH level. With these essential tips, you can promote the well-being of your fish and enjoy a thriving aquarium.


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