How to Lower pH in Aquariums Safely (2024 Guide)

Freshwater aquarium in pseudo-sea style
Freshwater aquarium in pseudo-sea style
Dr. Mollie Newton
Published by Dr. Mollie Newton PHD| Senior Editor
Last updated: May 9, 2024
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Aquarium aficionados need to monitor several factors in order to establish and sustain a prime fish tank.

From dissolved oxygen levels, ammonia and nitrate content, to pH, things can get a bit confusing for newcomers or aquarists who have been at it for some time.

If you take a reading and for some reason the levels are different than what you’d expect, just what should you do?

If you’ve ever wondered what exactly pH is, how it affects your tank, and how to lower pH in aquariums, read on!

Article Summary

  • pH levels in aquariums measure acidity and can range from 0 to 14, with 7 being neutral.
  • To lower pH, you can use water conditioners, reverse osmosis units, or natural methods like driftwood, peat moss, CO2 reactors, and Catappa leaves.
  • Maintaining stable pH levels is crucial for your aquarium’s health and can be part of regular maintenance.

What Does pH Level Mean?

Testing Water Using a pH Test Kit
Testing Water Using a pH Test Kit

While it may sound confusingly scientific, pH levels are simply a measure of acidity. The term stands for the “power of hydrogen,” and refers to the amount of free hydroxyl and hydrogen ions available in a liquid.

pH Levels

The pH scale runs from 0 to 14, with 7 being referred to as neutral pH, or H2O that has an even amount of hydrogen and hydroxide ions.

Water that has more hydrogen ions is known as being “acidic,” and has a pH level of less than seven. For instance, acetic acid has a pH of 4.76 and is quite bitter.

On the other hand, water with a pH greater than 7 is referred to as being alkaline in nature. Alkaline water is also called “basic,” meaning that it has more hydroxyl or hydroxide ions available.


PH levels will naturally shift throughout the day, meaning you may have a lower pH at one point than another as carbon dioxide levels change. Most fish are equipped to handle these natural, subtle shifts in their natural environments.

How pH Level Affects Aquariums

When it comes to your actual tank’s pH levels, things can get a bit more complicated. Considering that they live their entire lives immersed in it, the water chemistry of your tank can have a major impact on the health of your fish.

Some species such as tetras and discus may thrive in a very narrow range of pH levels. This means that when moving from one tank to another or initially placing them in your freshwater aquarium you’ll need to be especially aware of your aquarium pH levels.

Tank Setup

After getting your tank set up initially, a rapid shift in the pH of your aquarium can cause shock, especially to young or sick fish.

Fish Waste

Having a large accumulation of fish waste or a sudden influx of untreated tap water can quickly change things in your tank, causing sensitive fish to become more prone to illness or infection.


Considering that most fish will feel the effects of a major change to pH, it is a good idea to gradually lower the pH if you do find you need to change it. This will give your fish time to adjust properly, rather than all at once.

How Often Should You Test pH In An Aquarium?

digital tester dipped in a glass of water
A Digital Tester Dipped in a Glass of Water

Once a month is a good place to start for testing, but ideally, you’d want to test every two weeks. Keeping a log of the pH results can be a great way to track trends in your fish tank water and provides good insight into the overall effectiveness of your existing system.

Significant Changes in the Fish Tank

It’s a good idea to test your water after significant changes in your tank as well. Having a fish get sick or die, changing the water, or using medications are all instances when you may want to check your pH levels.

It’s important to note that pH levels can vary throughout the day through subtle shifts in the fish tank.

A higher reading may not necessarily indicate that something is wrong, but consistently higher readings show that you may need to lower the pH.

Adding New Fish to the Tank

Prior to adding new fish to the tank, it’s also a good idea to check your water to make sure that your newly added friend won’t have to adjust too much.


There are wide varieties of water quality test kit available for your aquarium to monitor pH. Some of these can even function to tell you whether you have excess nitrates or ammonia in your tank, in addition to giving you a pH readout!

What Is The Ideal pH For Aquariums?

Fish in the wild are adapted to a wide variety of water pH levels. Most salt water is fairly basic, at around 8.0 and therefore saltwater fish will prefer their aquarium water to have a similar pH.

Even some freshwater fish species such as African Cichlids come from naturally basic water at around 8.0, so as you can see things can be all over when it comes to ideal pH levels.

The key to determining what works best is to look at what species you’ll have in your fish tank.

If you’re designing freshwater aquariums for keeping fish such as plecos or tetras, you may want a lower pH of around 5-6.0, whereas a goldfish may prefer things to be more neutral at about 7-7.2 pH.

What Causes High pH In An Aquarium?

In most cases, seeing high pH in your tank water is the result of high levels in your source, be it tap water or other. Most natural processes from your fish will actually lower the pH level in your tank and sometimes result in a cloudy fish tank, as fish waste, leftover food, and decaying organic matter will begin adding carbon dioxide to the aquarium.

Having additional aquatic plants in your tank can create a higher pH level…

Having additional aquatic plants in your tank can create a higher pH level, as the natural respiration process takes in carbon dioxide without changing its alkalinity. This lowers the pH, which can occur slowly over time or quite rapidly in some planted aquariums.

When Should You Lower The pH In Aquariums?

Digital pH meter Dipped in water
Digital pH meter Dipped in water

In general, if your aquarium fish are not showing any adverse reactions you likely don’t need to change the water pH value.

Even if things are slightly off in measurement from what the stated ideal is, as long as your fish are behaving and appearing normally, they are likely just fine! The key is to keep your pH levels stable over time.

As with most issues that may arise, keeping a close eye on the normal behavior of your saltwater or freshwater fish is the best way to know when something is wrong.

Given that the creatures in our fish tanks can’t talk, it’s up to us as responsible aquarists to know when we may need to reduce pH or raise it.


If you have health concerns about the aquatic life in your tank, it’s never a bad idea to seek advice from a professional. These people are trained to provide veterinary advice based on the conditions in your tank and the organisms you’re raising, and will have the best knowledge and tools to help you move forward.

Symptoms of pH in the Aquarium to Watch For

  • Excess scratching on the side or bottom of the tank
  • Attempting to breathe at the surface
  • Uneven, rapid breathing or movement of the gills
  • Altered appearance such as pale or darkened skin

How To Lower The pH In An Aquarium

If you see consistent high measurements and symptoms in your fish indicating that you need to reduce pH, there are a few steps you can take. Some procedures on how to lower pH in aquariums may be more costly than others such as a reverse osmosis machine, and there are some more wonderful natural methods to use as well if that is of concern.

The first step is to identify the source affecting the water parameters in your aquarium.

If you know that it’s the tap water, you may want to consider using more heavy filtration or a chemical water conditioner.

Chemical Solutions

3 bottles of aquarium water conditioner
(1) Bottles of Aquarium Water Conditioner

Lowering pH with a water conditioner has the effect of lowering the pH without actually changing anything within the water. These chemical compounds act to bind to the free hydroxide ions in the water and keep them from altering the water chemistry in your tank.

While these store bought chemicals may work as a quick fix for the pH in your aquarium, if the problem is with the water source or elsewhere you may need a different solution such as a reverse osmosis water filter.

Reverse Osmosis Units

These handy units, also known as an RO filter, essentially work by creating pure water and allowing you to alter the chemistry from there.

These reverse osmosis machines or RO units may be slightly more expensive up front, but can make maintaining your aquarium water much, much easier overall.

The RO water generated by the reverse osmosis filter passes through a fine semi permeable membrane covered in pores, removing any water impurities, including arsenic, heavy metals, and pesticides.

This water can then be adjusted through chemical means to create the ideal environment for your personal fish tank and takes a lot of the hassle out of needing to lower the pH in your fish tank.


Your local pet store will be sure to have several different makes and models in stock, so make sure to do your research and determine which feeds your specific needs before purchasing!

How To Naturally Lower pH In Aquariums

If you’re looking for a method for adjusting pH while maintaining as much of a natural habitat as possible, there are a few ways to do so. From natural driftwood to adding peat moss, some of them can even add a lovely natural appearance to your tank.

Aquarium Driftwood

Adding driftwood is also great for adjusting pH. It does not only help to lower the pH but also provides natural hiding spots for different fish species.

Driftwood releases tannic acid over time, reducing the pH in your tank. However, releasing tannic acids also means that it may have the unintended result of darkening the water in your fish tank.

Closeup Piece of Driftwood for Aquarium with white background
Closeup Piece of Driftwood for Aquarium

Prior to adding it into your tank, it can be a good idea to soak your driftwood for a period of 24 hours or more, to get some of the free floating organics off. You can also find pre-treated driftwood for aquarium use available at most pet stores or online which will work just fine.

Peat Moss

Functioning similarly to driftwood, peat moss works to safely lower pH in your fish tank by releasing tannins and other organic compounds. Too much peat moss-treated water can have the added effect on fish tanks of turning the water a brownish color, which for some natural tanks can add an interesting color.

Peat moss can function as an additive to substrate in new tanks, allowing for additional pH buffering when first setting up your freshwater aquarium. You can use it as an additional filtration layer in a canister filter or add peat moss when first putting in your gravel or sand substrates to ensure that it has time to break down.

Using a filter bag with peat moss can allow the tannins to release effectively without the free floating particulate matter. This can help lower your water pH without leading to lots of floating moss bits in your aquarium.


Some areas may have naturally occurring peat moss present in the soil. Take care with peat moss harvested from the wild, as it may contain stray toxic elements or parasites.

CO2 Reactors

These machines work to add extra CO2 back into your tank. In an aquarium with lots of live plants, these can be invaluable as they provide the extra CO2 they need for respiration while simultaneously adding in a chemical that helps the pH inside your aquarium stable. As more CO2 dissolves into the aquarium water, more carbonic acid is formed, lowering the pH.

Catappa Leaves

Also known as Indian almond leaves, these function similarly to driftwood and peat moss by reducing pH in your aquarium with tannins. As the leaves break down, they will release tannins that will bond to the excess ions.

The advantage these may have over peat moss and driftwood is that they can be somewhat more precisely used and calibrated for your system. Over time, you can dial in the amount of leaves per gallon of fresh water in your tank.

In addition to safely lowering pH in your tank, Indian almond leaves may also provide antibacterial properties, which can come in handy if your fish are suffering from fin rot or you are raising vulnerable baby fish.

How To Raise pH In An Aquarium If It’s Too Low

Should you find that your aquarium pH is in fact too low, there are some ways to increase it. If you decrease aeration in your tank, you raise the amount of overall CO2 and lower the pH. Alternatively, adding in more aeration should raise the pH in your aquarium.

Additionally, adding in coral or limestone rock can increase the pH. These contain calcium carbonate, which will naturally raise the pH of your water as they dissolve.

The aforementioned RO filter system can be used to create more alkaline water if necessary as well, simply in the opposite direction.

Lastly, adding in additional plants will remove some of the CO2 and raise pH as they perform the process of respiration.

You can also watch this video below if you’re having a low pH in an aquarium.

How to Raise pH in Aquarium


Throughout today’s article, we’ve looked at what pH is, how it impacts the life in your fish tank, and how to safely lower pH levels or raise your aquarium’s pH depending on your needs.

While this may seem like a complicated bit of organic chemistry, once testing the pH in your aquarium becomes a regular part of your proper maintenance it should be a snap.

Feel Free to Share!

As always thank you for taking the time to read this post, I hope it has answered all of your questions about how to lower pH in aquariums safely.

Please feel free to share this information with any other fish fanatics you may know, and I wish you luck on your continued aquarium adventures!

(1) “I swear! It’s for my fish!!” by Moto@Club4AG is licensed under CC BY 2.0

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