How To Lower pH In An Aquarium

pH, or potential hydrogen, is one of the most critical components in any aquarium. Having the proper pH can mean the difference between life and death for a fish.

Some fish tolerate wide ranges in pH, while others can only handle slight changes. Aquarists must know what pH range their fish needs before buying them.

Most new hobbyists don’t know that they must understand basic chemistry to care for fish. Fortunately, pH is not hard to understand or manipulate.

Some simple testing can tell hobbyists what the pH levels are in their tanks. There are many ways to change the pH of the water, and most of them are natural and safe for fish.

What Is pH?

pH measures how acidic or basic water is on a scale of 1 to 14. 

A pH of 7.0 is neutral. A pH below 7.0 is acidic, and one above 7.0 is basic.

Essentially, pH is the concentration of hydrogen ions (H+) relative to hydroxide ions (OH-). The measurement of these ions is taken in an aqueous solution.

Do You Need To Understand pH?

Understanding pH may seem complicated. Still, every aquarium owner needs to understand some basic chemistry.

Mostly, aquarists need to know what pH levels their fish can tolerate. They must also know how to get their aquariums to those levels.

Getting the water’s pH to the right level requires aquarists to know how to lower and raise the pH.

What If The pH Is Off?

Aquarists measure pH on a scale of 1 to 14. These numbers can be deceiving, leading some hobbyists to believe that a change of “1” is not very big. Nothing could be further from the truth.

pH is measured on a logarithmic scale. Each number is greater than the next one by a factor of “10.” Any change in pH is a large one.

Aquarists must adjust their pH slowly. Making large changes too quickly can shock fish and may even cause death.

We recommend only raising or lowering pH by no more than 0.3 to 0.5 values at a time.

Why Is pH Important In An Aquarium?

The correct pH keeps fish healthy; it helps them resist disease and stress. It can boost their growth rates and make their colors appear more vibrant. It can even improve their attitudes.

A balanced pH helps keep the other chemical components in the aquarium stable. It prevents dangerous fluctuations in the tank that can make fish sick or kill them.

Water with a pH outside of the fish’s ideal range is sure to cause them stress. Stress eventually leads to illness and, sometimes, death.

A too-high pH damages the fish’s slime coat, which protects them from bacteria and parasites. It can cause chemical burns on the skin, eyes, and gills.

High pH reacts with the ammonia in the water, making it more toxic. Fish can suffer from ammonia burns or poisoning, which often causes death.

How Do You Measure pH?

The good news is that it’s easy to measure pH. Aquarists don’t need to understand everything about pH as long as they can measure it in their aquarium.

Liquid Test Kit

The most effective way for most home aquarists to measure pH is by using a liquid test kit.

We recommend using the API Master Test Kit, which is affordable and accurate.

Hobbyists add some tank water to a test tube with a few drops of reagent. After shaking the tube, the reagent will change the color of the water to show the pH.

The kit comes with a chart that shows what each color means. Aquarists can compare their aquarium’s pH to the pH their fish need. They can then make adjustments.

It’s best to sort out the pH before adding fish to the tank. Forcing fish to live in conditions that aren’t suitable for them can be stressful and even fatal.

Digital Monitors

Digital monitors are by far the most accurate way to test pH. They can measure pH to an accuracy of 0.01, which is far more precise than liquid test kits.

Still, digital monitors are expensive. These devices are usually better for experienced hobbyists caring for extra-sensitive fish. They are not necessary for the average hobbyist.

Test Strips

Another option for measuring pH is to use test strips.

Test strips are cheaper and easier to use. Yet, test strips are far less accurate than liquid test strips. We recommend avoiding these.

What Causes High pH?

Having a pH that is too low is far more common than having a pH that is too high. Still, natural processes can cause a pH that is too high and dangerous for fish.

The Source Water

Most often, the source water is the cause of too-high pH. The source water is the water that aquarists use to fill their tanks.

Many hobbyists use tap water to fill their tanks. Tap water is usually okay. Still, aquarists should test their water first. Tap water often has a very high pH — especially well water.

Too Many Plants

Another common cause of high pH is having too many plants or algae. While plants are great for the overall health of a fish tank, they can cause problems with the pH.

Usually, plants and algae have little effect on pH. Yet, when too many plants or algae are in the tank, the pH may rise to unsafe levels.

Plants and algae photosynthesize during the daytime when there is light. They use light to create energy; they turn carbon dioxide into oxygen.

At night, plants and algae do the reverse; they perform respiration. During respiration, they use oxygen to create energy and carbon dioxide.

The carbon dioxide increases while the carbonate alkalinity (kh) stays the same.

Usually, CO2 is slightly acidic. CO2 can cause pH to become basic without a change in carbonate alkalinity.

pH Altering Substrate

Another mistake that some aquarists make is using the wrong substrate. Some substrates naturally raise the pH of the water.

These substrates are generally reserved for cichlids and saltwater aquariums. New hobbyists unaware of these substrates may add them to their tropical tanks.

When Should You Lower pH?

Aquarists should lower the pH in their tanks when the levels become too high for their fish. Tropical species, like tetras and barbs, in too-basic water will become unhealthy.

How Can You Lower pH?

The good news is that there are plenty of ways to lower pH.

First, aquarists should determine what is causing the spike in their pH. From there, they can determine which method is best for lowering it.

For quick fixes, aquarists can add pH-buffering chemicals to their water. Hobbyists often rely on driftwood, catappa leaves, and peat moss for longer-lasting results.

Changing The Water Source

Many hobbyists have tap water high in carbonate (kh) or general hardness (gh).

General hardness measures the amount of calcium and magnesium ions in the water. Carbonate hardness measures the amount of carbonates and bicarbonates in the water.

Having kh and gh levels that are high simultaneously results in high pH.

Often, changing the water going into the tank is an easy fix. While changing the source water can be expensive, it’s usually the easiest fix for high pH.

Sometimes, aquarists simply need to buy a good filter for their tap water.

Other times, they may need to change their source water completely. Buying bottled water from the store is a good option — avoid distilled water.

Choosing reverse osmosis (RO) water is another option.

Reverse Osmosis (RO) Water

Many aquarists who struggle with high pH prefer to use reverse osmosis (RO) water.

Reverse osmosis is a purification process. It removes all contaminants and minerals from the water. It leaves the water completely pure with neutral pH (7.0).

Reverse osmosis filtration systems can get expensive, though they are worth the investment. They also need regular maintenance.

These systems are not practical for most hobbyists. Those with large aquarium systems or especially sensitive fish usually find them valuable.

Some local fish stores (LFS) sell reverse osmosis water as well. Hobbyists simply need to bring in buckets to transport the water.

Buying RO water from the store is usually much cheaper than installing a system in the home. The only downside is that the water can be heavy to transport.

Performing Water Changes

Sometimes, when the pH gets too high, all aquarists need to do is perform a water change.

A water change will only lower the tank’s pH if the source water already has a lower pH.

Performing water changes with water that has a lower pH is essential. On average, hobbyists should complete water changes once every two weeks.

Why Topping Off The Aquarium Isn’t Enough 

Topping off an aquarium with water while never doing water changes is a big mistake.

First, forgoing water changes cause the tank to get dirtier and dirtier. The ammonia and nitrites will build up and will make the fish sick.

Secondly, as the water evaporates, the minerals from the water stay behind. Water changes remove these excess minerals to keep the mineral content balanced.

Without water changes, the mineral content continues growing. Excess minerals cause the pH to continue rising.

What If Water Changess Aren’t Enough?

A water change may or may not be enough to lower the pH to safe levels. Aquarists can go on to use the methods described below if a water change is not enough.

Even if a water change is insufficient, it will still lower the pH somewhat. Remember that even a drop of 0.3-0.5 is significant. Give the fish time to adjust to the change in water before adding any of the below methods. Lowering the pH too quickly can shock and kill fish.

Driftwood

Adding driftwood to the tank is one of the easiest and most effective ways to lower pH.

Driftwood contains tannins, a natural chemical compound that resides in many plants.

Tannins lower pH slowly; the change won’t shock the fish.

The wood continues to release tannins for a long time. Using driftwood in the tank is one of the most permanent ways to alter pH.

Driftwood naturally exists in many rivers and lakes. It lowers the pH of these massive water systems. It’s why many tropical freshwater species are used to slightly acidic water.

The Benefits Of Driftwood

Another benefit to using driftwood is that it adds to the aesthetic of any tank. It makes aquariums look more natural and provides hiding places. As the wood decays, it provides food for many of the tank’s inhabitants.

Tannins also boost fish’s immune systems and help them stay healthy.

The downside for some aquarists is that tannins make the water brown. Still, the change in water color is a small price to pay for the pH-lowering properties of the wood.

Choosing Your Driftwood 

It’s best to choose dark woods, like Mopani wood (Colophospermum mopane). Light-colored wood, like cholla wood, doesn’t change the pH much.

* Aquarists should avoid boiling driftwood if they want its pH-lowering properties. Boiling the driftwood removes the tannins that lower pH. *

Peat Moss

Adding peat moss to the aquarium is another natural method of lowering the pH.

Measured by weight, peat moss contains more tannins than driftwood.

Like driftwood, the tannins in peat moss lower the aquarium’s pH. They also boost the inhabitants’ health. The tannins turn the water a murky brown, though many hobbyists like this look.

Peat moss is great because it slowly decays over time, like driftwood. Fortunately, the decay of peat moss does not cause the ammonia in the tank to rise. Instead, the decaying material sinks into the substrate and feeds the live plants.

Adding Peat Moss To The Aquarium 

Peat moss floats — adding it to the aquarium can be a pain.

One of the best ways to use peat moss is to mix it with the substrate. Doing so creates a grass-like effect at the bottom of the aquarium. It also prevents the moss from floating to the top.

Another option is placing a peat moss ball inside a mesh bag or a piece of pantyhose. The porous nature of these items allows the tannins to leech into the water.

Tying the bags to rocks or decorations at the bottom of the aquarium is another option. Make sure to secure the bags somewhere there is plenty of flow. Placing them inside a filter is the best way to get the pH to decrease slowly.

Cautions

Hobbyists need to use caution when using peat moss. The acidity of peat moss varies; it can be difficult to tell how much the pH will drop and how fast.

Aquarists should test their water daily after adding peat moss to watch the pH levels. Keep testing the water until the pH levels out.

The size of the tank, how many plants the tank has, and other factors will determine how much peat moss lowers the pH.

Avoid using peat moss in an aquarium of fewer than 10 gallons. There is not enough water to buffer the tannins, and the pH can drop to fatal levels rapidly.

Indian Almond Leaves

Terminalia catappa, or Indian almond leaves, are another option for lowering the pH in a tank.

Like peat moss and driftwood, these leaves release tannins.

The tannins turn the water brown and boost the health of the fish. Many aquarists specifically add these leaves to their tanks to help heal sick fish.

The Benefits Of Indian Almond Leaves

It is a bit easier to dose a tank with Indian almond leaves than with driftwood or peat moss. Aquarists should add one leaf for every 10 gallons of water. Doing so will slowly decrease the pH.

Like driftwood and peat moss, these leaves offer food for some organisms as they degrade.

Adding Indian Almond Leaves To The Tank 

Aquarists can place these leaves on the water’s surface, where they’ll float. They can also tie them into bundles using a bit of string to keep them from wandering. Some hobbyists even place them inside their filters. 

pH-Buffering Chemicals

Using chemicals is often the most unreliable and dangerous way to alter the pH in an aquarium. Yet, they are one of the most common methods.

Chemicals aren’t permanent. Aquarists must add them regularly to maintain the proper pH.

Determining how much of the chemical to add to the tank can be challenging.

Those using chemicals cannot rely on the dosage suggested on the bottle. The only time the bottle dosage is accurate is if aquarists are using RO water, which is neutral.

Aquarists using tap water must perform tests to determine how much of the chemical to add.

The composition of tap water varies by location. It’s not only the pH that varies, either. Different locations have different amounts of cations and anions. These affect how the pH buffers react with the water and how it adjusts the pH.

CO2 Reactors

These devices are not explicitly used to lower pH. They help with the health of many live plants that need high levels of CO2.

CO2 reactors provide a constant stream of CO2, which plants need for growth.

CO2 is slightly acidic and helps lower an aquarium’s pH. Reactors help keep the pH in an aquarium stable and prevent dangerous fluctuations.

FAQs

What Is The pH Of Saltwater?

Saltwater generally has a pH of 8.0, making it slightly basic. Most saltwater organisms will tolerate a pH between 8.0 and 8.4, though it depends on the species.

Most saltwater organisms cannot handle huge variations in pH. 

What Is The pH Of Freshwater?

Most freshwater fish can handle a wider-ranging pH than saltwater fish.

The pH of freshwater depends on many factors. Most freshwater systems are slightly acidic to neutral. Other, more extreme systems are somewhat basic.

For instance, most fish that aquarists keep will need a pH between 6.8 and 7.8. Most cichlids need slightly basic water because they come from unique habitats. They need a pH closer to what saltwater fish tolerate.

Which Fish Are Best For High pH Aquariums?

Most tropical freshwater fish prefer a neutral, slightly acidic, or slightly basic pH. Still, there are plenty of species that thrive in a high-pH environment:

• Platys
• Congo tetras
• Guppies
• Mollies
• Flagfish
• X-Ray tetras
• Odessa barbs
• Turquoise rainbowfish
• Dwarf neon rainbowfish
• Golden wonder killifish