What Causes PH Changes and How to Fix Them

Kate Barrington
by Kate Barrington

What’s the chemistry like between your aquarium fish and the water they swim in? Keeping the pH of your tank water is a vital element when it comes to keeping your fish healthy.

In order to keep your aquarium fish happy and healthy, you need to maintain high water quality in your tank. Having a filtration system in place and performing weekly water changes will go a long way toward preserving water quality, but you also have to think about various aspects of water chemistry. The pH level in your tank is important and it may change from time to time – when it does, you need to know what you can do to get it back to normal.

Causes of Change in pH

The pH of your tank water is a measure of the alkalinity or acidity and it is measured on a scale from 0 to 14. A neutral pH is measured at 7.0. Any measurement below 7.0 is said to be acidic while pH values above 7.0 are alkaline. There are a number of factors that contribute to the pH level in your tank including the trace mineral content, the type of substrate you use, and the chemical concentration in your tank water. If any of these things change, it could lead to a change in the pH value of your tank water. Other things that might cause a change in pH include the use of certain medications, the failure of your filtration system, or even certain objects or decorations in your tank (like driftwood). The key to dealing with changes in pH is to identify the cause.

When finding the right pH level for your aquarium, neutral is not necessarily the sign that it is optimally balanced for your fish. Different species of fish are suited to thrive at different pH levels. Therefore, you need to take the time to better understand the fish that you are caring for.

If you already have an aquarium, you will need to do some research into the different species that you already have present. This may lead you to make some changes to your current tank arrangement if you find that their needs are too different from one another. But, if you are just starting your aquarium, you can avoid this problem. Choose a variety of fish that are all similar in their pH preferences. For example, if you love a species that thrives best in a pH8, try researching others that are also adept at living in that environment. This will ultimately make it easier for you as you work on maintaining your tank.   

Related: What You Need to Know About the Nitrogen Cycle

Why Are Changing pH Levels Dangerous for Your Fish?

When the pH level in your tank suddenly swings in a different direction, it makes it difficult for your fish to properly control the amount of water that they are holding in their bodies. This can quickly cause your fish to be either dehydrated or over-hydrated, which can lead to serious health complications. While fish can handle mild or slow changes in pH, a sudden or significant change can lead to trouble. In the most serious examples, it can be fatal. This is why it’s so important to do what you can to prevent these wild swings and keep the pH level balanced.

Tips for restoring pH in the Aquarium

The pH in your aquarium can go one of two ways – up or down. If the pH in your tank suddenly drops, there are several things you can try to raise it:

  • Perform a water change. If you don’t keep up with regular water changes in your tank, the chemical balance will change and that will affect the pH. Performing a water change will help to restore the natural pH level of your tank water.
  • Changing your substrate. Certain types of substrate will naturally raise the pH in your tank. Things like crushed coral or limestone have this effect but keep in mind that it will be hard to control the degree to which these substrates impact your pH.
  • Increase the aeration in your tank. When you increase the oxygen levels in your tank water you will be decreasing the carbon dioxide levels and that will increase the pH. Adding an airstone to your tank or installing a more powerful filter can have these effects.
  • Using baking soda. If you need to change the pH of your tank water, adding baking soda may help. It is important that you don’t add too much at once, however, because sudden changes in pH can be deadly for your fish. Do not add more than 1 teaspoon per 5 gallons and make sure it is thoroughly dissolved in water before you add it to the tank.
  • Decorate with limestone, coral sands, and gravels or shells. Your choice of decoration in the tank can have a direct impact on the pH level of the water. These items all release carbonates into the water slowly while they are there, increasing the pH levels and creating more alkaline water. If you want to enjoy the benefits but aren’t a fan of the look of shells or limestone, you can also place crushed shells or limestone chips in a media bag to place in the tank.

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These are just a few of the ways you can increase the pH in your tank. If you need to lower the pH in your aquarium, try one of these methods:

  • Add peat moss. Using peat moss as the substrate in your tank or simply adding some to your filter may help to lower the pH in your tank – just be sure not to lower it too much at one time.
  • Increase carbon dioxide. As you already learned, low levels of carbon dioxide frequently correlate with higher pH levels. You can expect the opposite to be true as well. To help lower pH in your tank, increase CO2 levels by reducing aeration or by adding supplemental CO2.
  • Add driftwood to your tank. Driftwood contains tannins which not only stain your tank water brown but also lower your water pH. Just be careful about how you use it.
  • Incorporate Catappa leaves into your tank. These decorative leaves are popular among fish keepers due to their anti-fungal and anti-bacterial properties. When first purchased they are dried and will float on the top of the tank. But, in time, they will sink down to join the rest of your décor. They work similarly to bogwood and peat to make the water acidic.

Using Buffers to Prevent pH Problems

Aquarium or fish tank buffers are chemicals that are designed to regulate the pH levels in your tank. They do this by addressing both acid and alkali, helping to the levels balanced. While this isn’t guaranteed to stop all pH changes, they do prevent the big pH swings that may happen in an unregulated tank which can cause serious harm to some fish.  

There are many different chemical buffers on the market, but you are going to want to pay careful attention to which is best studied for your aquarium. This will depend on the environment that you are creating (live plants versus artificial plants), whether you are caring for a saltwater or freshwater tank, and the pH needs of the individual fish that you are keeping.  

Maintaining proper water chemistry in your aquarium is a balancing act. By testing your tank water on a weekly basis you can establish a baseline for the “normal” water chemistry of your tank. Then, if you get a test result outside the normal range, you will know that something is wrong and you can take steps to fix it. Just be sure not to make any sudden changes to the water chemistry in your tank because your fish might not be able to handle it.

Kate Barrington
Kate Barrington

Kate Barrington is the loving owner of two cats (Bagel and Munchkin) and a noisy herd of guinea pigs. Having grown up with golden retrievers, Kate has a great deal of experience with dogs but labels herself a lover of all pets. Having received a Bachelor's degree in English, Kate has combined her love for pets and her passion for writing to create her own freelance writing business, specializing in the pet niche.

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