How to Lower the pH in an Aquarium

How to Lower the pH in an Aquarium

Keeping healthy fish means maintaining healthy water. Aquarists know that maintaining a fish tank requires careful measurement and adjustment of your water quality and that fish need certain pH levels to stay happy. But what is pH, and how can you lower it when necessary? Wondering how to lower the pH in an aquarium? Let’s look at what pH is, how to measure it, and how to reduce an aquarium’s pH.

What is pH in Aquariums?

The term “pH” stands for “power of Hydrogen.” It’s a measure of how acidic water is on a scale of 1 to 14. Neutral water (pure H2O) has equal amounts of hydrogen and hydroxide ions, so it’s measured at 7, right in the middle of the scale.

When water has a pH higher than 7, it is alkaline or basic, and when it is lower than 7, it is acidic.

The pH of water is affected by minerals or compounds dissolved in the water, plant growth and respiration, and other factors and processes in the natural world.

In other words, natural pH changes all the time and is different in different places, different seasons, and even different times of the day.

There is no consistent measure of pH in natural water, and almost no natural water has a perfectly even pH of 7.

Aquarium fish come from all over the world and are native to a wide range of environments. It’s essential to know the pH level your fish need and choose fish that can live together in similar water conditions.

Then you need to test and maintain the pH in your aquarium to keep your fish happy and healthy.

How to Test Your Tap Water’s pH

To keep a healthy aquarium, you need to know the pH of the tap water in your house. If you get your water from a municipal water supply, most cities regulate water quality to require a pH of 7-9.

However, as water travels from the facility to your house, it can pick up minerals and particles as it travels through pipes and water mains. You need to pH test water every time you intend to use it in your aquarium. Here’s how:

Measure the pH of Your Tap Water With pH Papers

You may remember using litmus paper in science class in school and think you can use them for your aquarium.

Litmus papers only indicate that water is acidic or basic and don’t actually give you a helpful measure if you need to correct pH for an aquarium. Instead, use pH papers. When you dip a pH test paper strip into water, it changes color.

These paper kits include a color chart with colors from 1-14, so you can place your test strip against the color chart and determine your water’s pH.

Measure the pH of Your Tap Water With a pH Meter

A pH meter is the fastest and most precise way to measure pH. Litmus strips only indicate whether water is basic or acidic, while pH paper only measures to the nearest whole number.

A pH meter is more precise, with digital readings to decimal points. They are fast to use and easy to read.

When is it Necessary to Lower pH in Aquariums?

If you have an aquarium, you frequently need to test the pH. Some of the key times to test pH in an aquarium are:

  • Before you purchase a new fish. Check that your aquarium’s pH is within 0.2 of the pH the fish is currently living in, and adjust it to prevent shocking a new fish
  • When there is fish illness or death. If your fish are showing signs of disease, check your aquarium water’s pH and adjust it if necessary
  • When using medication. If you are treating or medicating your fish, check pH before and during treatment and again a week afterward
  • Every two weeks as part of regular maintenance. Test your pH on a regular schedule, preferably at the same time of day every time. Keep a logbook so you can note changes over time

If your aquarium pH is relatively stable and your fish seem healthy and happy, you don’t need to adjust the water’s pH. If the pH changes dramatically or your fish seem unhealthy, it’s probably time to adjust the pH balance.

How to Lower the pH in an Aquarium

How to Lower pH in Aquariums: Recommended Methods

If your aquarium pH is too high, there are many ways to lower it. Some methods adjust it quickly to reach the desired levels, while other techniques help reduce it gradually and keep it lower over time.

Here are the best ways to lower pH in an aquarium.

Chemical Additives

There is a wide range of chemicals that will lower an aquarium’s pH very quickly. It is recommended to only use chemicals in an emergency because abrupt pH changes can be harmful to fish.

It is better to lower it gradually and take steps to keep aquarium pH stable over long periods.

Peat Moss

Peat moss is an excellent addition to an aquarium. It absorbs minerals and softens water while naturally releasing gallic and tannic acids that lower pH.

For long-term effectiveness and stability, peat moss needs to stay submerged in the aquarium and added to the filter or used as part of the substrate.

You can also use peat moss in a separate container to pre-treat water for use in an aquarium. Peat moss is dark brown and will tint the aquarium water, turning it a yellow-brown “tea” color.

To reduce or prevent this effect, boil peat moss to remove contaminants, then soak it in a bucket of water for several days before using it in your aquarium.


Driftwood is beautiful aquarium décor and safely and naturally lowers pH over time. Like peat moss, driftwood slowly and naturally releases tannic acid. Also, like peat moss, driftwood can discolor the water.

To use driftwood in an aquarium, you can’t just pick up random wood and place it in your aquarium.

It is best to buy pre-cured driftwood from an aquarium supply shop. Then you know that it’s aquarium-safe, properly cured to prevent rotting, does not have harmful microorganisms, and hasn’t been cleaned with detergents that may be harmful to your fish.

Reverse Osmosis

Reverse osmosis filters purify aquarium water with a membrane that allows only the smallest particles to pass through. This filters out a wide range of impurities and produces “neutral” water with a pH of 7.

However, when aerated, this neutral water will absorb carbon from the air and quickly achieve a pH of about 5-5.5.

Reverse osmosis units are expensive and occasionally require new replacement filters. However, they are a great way of cleaning aquarium water and maintaining a low, stable pH over long periods.

Catappa Leaves

Catappa (also known as Indian Almond) leaves are another natural way to lower the aquarium’s pH. Like peat moss and driftwood, they release tannic acid that lowers pH and can discolor aquarium water.

Fans of catappa leaves also note that they have many other benefits for fish. They release chemical compounds that are high in antioxidants, flavonoids, and saponins that help improve immune response and disease resistance and reduce inflammation.

It helps fish resist bacteria and germs and are even effective at helping fish reduce parasite and fungal infections. They are most commonly used in creating blackwater aquariums but can also be added to water in a separate container, treating the water before use in an aquarium.

It is more important to have a stable, consistent pH level over time than to achieve the exact pH recommended for your fish. Most modern aquarium fish are tank-bred and tolerant of a broader range of pH levels than wild fish.

Tank-bred fish can often be comfortable in pH ranges from 6.5-7.5 or even higher, as long as the level is stable and doesn’t change quickly.

If your pH readings are within .5 of the recommended level for your fish, and the fish seem happy and healthy, there is often no need to adjust the aquarium’s pH.

Despite the need to maintain consistency, remember that pH readings will also fluctuate naturally, depending on several factors. It’s common to see pH readings vary by .2-.4 over a day.

This is why keeping a logbook and testing at the same time every day will help give you a more accurate picture of the pH of your aquarium and help you better track it over time.


Maintaining a healthy pH requires consistent measurement and long-term solutions. There are many ways to measure, adjust, and lower the pH in an aquarium, so you can keep it stable over time and provide a healthy, consistent environment for your fish.

The simplest and most natural ways to lower pH use the natural composition and processes of wood, moss, and leaves, but they are prone to staining your aquarium water.

If you want stable pH and crystal clear water, consider using a reverse osmosis system.