How to Lower or Raise the pH in Your Aquarium – 11 Different Ways

As a fish keeper, one of your key roles is to make sure your water is suitable for your fish.

In addition to factors such as making sure they have freshwater or saltwater, the temperature is correct, monitoring hardness, ammonia and nitrate levels, you also need to consider the pH of the water in their tank.

But the water you get from your tap – or any other source – may well not be pf the right pH that your fish require. Therefore, you need to know how to lower aquarium ph in some circumstances, or how to raise it in others.

How to lower or raise pH in your aquarium, written beside bright yellow and blue fish in a tropical tank

If you’re new to the hobby, you might not even know what pH is, let along how to raise or lower the pH in your aquarium.

In this post, we’ll tell you everything there is to know about fish tank water pH, from what it is to what to do to change it.

What is pH?

In short, pH is the measurement of acidity or alkalinity in a substance, but it’s a little more complicated than that.

When talking about the pH in your aquarium, remember that all water is made up of hydrogen and oxygen—H2O. Some of these molecules will split up, so you’re left with pure hydrogen (H+) ions, as well as hydroxide (OH-) ions. H+ ions are acidic, whereas OH- ions are alkaline (or “base”).

The pH of your aquarium is a measurement of the hydrogen and hydroxide ion concentration of the water, thus telling you its relative acidity.

What is the pH Scale?

The amount of H+ and OH- ions in substances is huge. For instance, a highly alkaline solution can have one hundred trillion times more hydroxide ions than a highly acidic solution.

So, rather than dealing with absurdly large numbers, we use the pH scale to describe the concentration of ions and the acidity or alkalinity of a substance.

The pH scale goes from 0 to 14. The lowest numbers are the most acidic, and the highest number is most alkaline.

A substance with a pH of 7 is neutral, whereas anything higher is alkaline and anything lower is acidic. A pH of 7.1 is very slightly alkaline, whereas a pH of 14 is highly alkaline. On the other side of the scale, a pH of 6.9 is slightly acidic, whereas a pH of 0 is highly acidic.

What Influences the pH in the Aquarium?

A range of factors can affect the pH inside of a fish tank. Here are some of the most common:

  • Adding driftwood to your tank can lower the water’s pH.
  • Coral ornaments and substrate can raise the pH of your aquarium.
  • When you change the water in your tank, it may have higher or lower pH afterward, depending on the pH of the water you add (soft water has a lower pH).
  • Overstocked aquariums often have a lower pH, due to increased waste.
  • Hard water has a higher pH than soft water, so your tank is likely to have an increased pH if you live in a hard water area.
  • High levels of nitrates will cause a decrease in pH levels.
  • Water purifiers lower pH—and are therefore beneficial if you have hard water.
  • Decreased aeration lowers water pH and an increase in aeration may raise pH.

What is Low pH?

As we touched on above, low pH (anything below 7) is acidity. That’s not to say that anything with a pH under 7 is the type of acidic substance that would burn the skin, it merely has a higher concentration of H+ ions than OH- ions.

What is High pH?

High pH (anything above 7) is alkalinity. This simply means that a substance has a greater concentration of OH- ions than H+ ions.

What is the Ideal pH Level? (It Varies!)

You might be wondering what the ideal pH is for an aquarium. Unfortunately, there’s not a simple one-size-fits-all answer—it depends on a range of factors, such as the fish you keep and the plants you grow.

It’s also important to remember that it’s better to have a stable pH that’s 0.1 to 0.4 higher than the “optimum” pH for your tank than have a pH that’s continuously fluctuating while you chase that perfect pH.

That said, here’s the pH you should be aiming for with some common aquarium fish.

  • Goldfish can survive in water with a pH of between 6.0 and 8.0, but you should ideally aim for between 7.0 and 7.4.
  • Betta fish prefer neutral or slightly acidic water—between 6.5 and 7.0, ideally.
  • A standard community tropical tank should have a pH of around 7.0, as this suits a wide range of fish.

How to Test the pH of Your Water

Now you know a bit more about aquarium pH, you might be wondering how to test the pH of your water?

While there are many pH test kits on the market, we recommend using one of the master test kits from our roundup, or the API pH Test Kit as it’s affordable and straightforward to use

To find out the pH of your water using the API pH Test Kit, simply fill up the included test tube with a sample of water from your fish tank. Make sure the tube is filled to the line marked on its exterior. Add three drops of the test solution, put the cap on the test tube, give it a shake, and wait for the water to change color.

Finally, compare the color of your water to the color chart provided to find out the pH of your aquarium water.

What are the Effects of pH in the Aquarium?

So, the pH of the water in your aquarium can be too high or too low, but what effect does it have on your fish?

Both too-high alkaline and too-high acid can affect your fish negatively, so it’s important to look out for the signs.

High Alkaline

Water that’s high in alkaline (has too high a pH) can damage your fish’s gills and ultimately lead to death.

You’ll often see fish darting back and forth—more so than usual—when their water has too high a pH, so be sure to test if your fish are exhibiting this behavior.

High Acid

If your aquarium is high in acid (has a low pH) it increases toxic elements and can cause an excess of mucus in your fish.

Like excessively high alkaline water, high acid water can kill your fish. Signs the pH of your aquarium water is too low include eye damage, gasping, and thickening of the skin and gills.

How to Lower Aquarium pH Safely

If the alkalinity in your tank is too high, you need to lower it to restore optimal ph for your tanks inhabitants. Luckily, there are several ways to do this safely.

Peat Moss

Adding clumps of peat moss to your water can help naturally lower the pH in your aquarium by releasing tannins and gallic acid, which filter out contaminants and lower alkaline levels. The trouble is that it can discolor water, so it’s not everybody’s first choice.

You should also be aware that peat mining destroys peat bogs, which are a dwindling natural resource, so it’s not the most environmentally friendly option.


If you want the benefit of those tannins, but without the environmental impact, try adding driftwood to your aquarium. Not only does it lower pH level, but it also makes an attractive tank decoration and a nice hiding spot for your fish.

Make sure you choose driftwood prepared for aquarium use, as pieces designed to go in reptile tanks may contain chemicals that would leach out into your water.

Catappa Leaves

Also known as “Indian almond leaves,” catappa leaves are a natural water purifier and great for lowering the ph.

Simply add them to your tank, and they release tannins that reduce pH levels. If you don’t want leaves floating around in your tank, you can soak them in water for several days, strain them out, then add the water you soaked them into your tank.

However, like other options that involve tannins, catappa leaves will stain your water with a yellow tinge.

Reverse Osmosis

Reverse osmosis is a filtering/deionizing process that removes impurities from water and will lower the ph levels too. Reverse osmosis is entirely safe and natural and won’t discolor your water, like many other methods.

However, a reverse osmosis filter unit can set you back a couple of hundred dollars.

Water Change

If you live in a soft water area or can filter your water to soften it, your tap water can be used to lower aquarium ph naturally.

If your fish tank is suffering from a high pH, simply adding soft water during a water change means you will lower the overall pH in your tank.

Substrate for Live Plants

A substrate meant for planted tanks can help naturally lower the ph level, helping to maintain it around 6.0 to 6.5.

Even better if you actually want to keep a planted aquarium, as you’ll have the right substrate FOR THE JOB.

How to Raise pH in Your Aquarium Safely

If you have the opposite problem and your aquarium is too acidic, there are many ways and methods for raising the ph.

Crushed Corals

Crushed corals and mollusk shells contain calcium carbonate, which acts to raise pH.

You can add bags or crushed corals to most aquarium filters, though you will have to experiment with the correct amount to add to reach your desired pH levels.

Dolomite Chips

Though you might not know them by name, you’ve probably seen dolomite chips around.

If you’ve ever used that brightly colored, slightly rough-textured aquarium gravel, you’ve already been using dolomite chips.

Dolomite is a mineral rich in magnesium and calcium, both of which can help raise the ph level in fish tanks.

You can add dolomite chips in a bag to your filter or use them as a substrate.


The calcium carbonate in limestone leaches into the water and helps to raise the levels of alkaline in your aquarium. You can use limestone rocks as aquarium decoration, creating caves or other hiding spots.


Consider growing macroalgae in your aquarium to raise the pH—not only does it do an excellent job of increasing alkalinity, but it also looks great and provides a more enriching environment for your fish.

Macroalgae raise pH by reducing carbon dioxide and oxygenating the water. What’s more, it’s incredibly cheap and easy to grow.

Baking soda

Another surefire way of increasing the pH in your aquarium is adding baking soda. It isn’t our first choice, however, as it’s very easy to add too much, which could cause a pH spike and make your fish unwell or even kill them.

If you do choose to use baking soda, remember to use it sparingly. It’s also not a long-term fix, so you’ll have to keep adding more to keep the pH levels stable.


Both high and low pH can be damaging for your fish, so it’s important to monitor the levels in your aquarium.

While you should know what signs to look out for that suggest the pH in your tank may be too high, by the point your fish exhibit these symptoms, they’re already suffering, so the best thing to do is regularly check the pH of your tank, at least once a week.

B Hamilton

Hey there! I'm Brian, a lifelong enthusiast and fish keeper with a wealth of knowledge and experience on freshwater aquariums, that I love to share on this site. If you have any questions or need any help, please do ask in the comments section below, I'd love to hear from you and will help where I can.