Whether you are a serious fishkeeper or just a gentle hobbyist, you should familiarize yourself with the subject of “Fish Tank pH Levels.”
Water pH (power of hydrogen) is measured on a scale of 0 (acid) – 14 (alkaline), with 7 being neutral. Optimum pH levels are between 6.5 and 8 for most freshwater fish. When fish tank pH levels become too high or low, fish can become stressed and even die.
If you find pH levels confusing, you are not alone. It is essential to understand some of the terms used when discussing a fish tank’s pH level, but it can also become overwhelming.
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This article will explain aquarium pH levels in small, easy-to-digest chunks and in an easy-to-understand way, so read on to become an instant expert.
What Is pH In A Fish Tank
pH in a fish tank is the acid or alkaline level in the water. The chemical makeup of the water in your aquarium is vital to keep your fish healthy so they can thrive. Matching your fish tank’s pH level to what your fish are used to in their natural habitat will create a more comfortable environment for them to live in.
Fluctuations in a fish tank’s pH level can be caused by decaying fish food, fish waste, and decaying plant matter, which is why it is important to cycle your aquarium before adding fish, as fishless cycling will reduce fluctuations.
The pH level will fluctuate to some degree both in the wild and in freshwater aquariums. Most fish are used to small fluctuations, but more significant changes can be devastating to the health of your fish, your plants, and the overall biological health and ecosystem of your aquarium.
What does pH Stand For
pH stands for “Pondus Hydrogenii,” which is Latin for the “weight of hydrogen” however, most people believe that pH stands for “Power of Hydrogen” or “Potential of Hydrogen,” and these terms have become more commonly used. Either way, the “H” is capitalized because hydrogen is an element on the periodic table written as “H.”
pH was first termed and described by Danish biochemist Soren Peter Lauritz Sorensen in 1909.
What Does pH Measure
pH is a measure of how basic or acidic an aqueous solution is, based on the number and activity level of hydrogen ions.
Hydroxide ions (a combination of hydrogen and oxygen) also play a part in the variance of pH levels.
An acidic solution has more hydrogen ions, while basic solutions have a deficiency of hydrogen ions. The more hydrogen ions in relation to hydroxide ions, the more acidic a solution becomes. You will notice I have used the word “basic” instead of “alkaline,” which I will explain later on in this article.
The pH scale runs from 0-14, with 7 sitting in the middle, indicating neutral pH. Each 1 point movement on the scale in either direction is 10 times the previous measurement. It is important to understand this 10x factor because the further you get from a neutral pH, the more severe each 1 point change becomes.
I hear the question, “What is pH in water?” quite a lot, and even with an explanation such as the one above, they are no closer to understanding. The easiest way to understand pH is by using the pH scale.
An excellent visual scale like the one below will help. The below scale gives you an idea of the level of acidity or alkalinity of many well-known foods or fluids and where they sit on the pH scale, with pure distilled water sitting in the middle of the scale at neutral pH.
As a fishkeeper, a pH number scale like this is all you will need to understand pH levels at their most simple. Don’t get me wrong, there is far more to understanding how pH works, and I will cover some of it later in this article.
Your main concern is to ensure your fish tank water is not too acidic or alkaline (basic), which will harm your fish. By understanding the pH of your water, you will know whether you will need to raise or lower it.
Most pH test kits are easy to use and will return a result comparable to the pH scale.
Becoming familiar with pH values is an important step. You will need to know the ideal pH level for your fish species, why pH can rise or fall, and how to create an environment with a stable, balanced pH.
Why Is High pH Called Basic
You will have probably noticed me referring to a high pH as both “alkaline” and “basic” throughout this article. I will give a very brief explanation, but it’s not necessary to understand the difference between alkaline and basic as an aquarist.
Definition of Basic
In chemistry, a base is a water solution of any chemical compound that produces a solution with a hydrogen ion concentration lower than that of pure water. Sodium hydroxide and ammonia are two examples. Bases are the chemical opposites of acids. Bases reduce the hydrogen ion concentration in water, whereas acids increase them. Acids and bases neutralize each other when they combine.
Definition of Alkaline
In chemistry, the term alkali refers to salts (ionic compounds) containing alkali and alkaline earth metal elements that accept a hydrogen ion in solution. Alkaline bases are best known as bases that dissolve in water. Alkali metals react vigorously with water, producing hydroxides and releasing hydrogen. The reaction with air covers the surface of the solution with oxides. In nature, ionic compounds (salts) contain alkali metals but never in a pure state.Source: Sciencing.com – Alkaline VS Basic
As far as this article, I will refer to a high pH as both alkaline and basic so that you will become familiar with both terms.
If you have been reading about pH levels, you will have probably come across the term “pH buffers” or “pH buffering,” This is a subject worth understanding as it will help keep your aquarium pH stable.
What Is An Aquarium pH Buffer
In short, buffering is the ability of water to resist changes in pH. Many chemical compounds can be used as aquarium pH buffers to protect against rising or falling pH levels.
Creating a stable pH is the perfect solution within any fish tank, and you can easily achieve it.
Again, I will not hit you with a ton of information about how chemical compounds interact, although this is generally how buffering works.
Water with a high mineral content is usually harder and more alkaline (higher pH), whereas water with a low mineral content is softer and more acidic (lower pH).
Water that is too alkaline would require the addition of acid to balance it out; however, the high level of minerals found in this type of water would buffer against the acid, causing very little change to the pH.
To remove this issue, you would first need to remove some of the mineral content before adding an acidic compound such as peat or a commercial pH decreaser.
How do you remove minerals from water? One method is reverse osmosis, which filters minerals from the water using a special device. Another way of removing minerals is by changing and adding water back with lower mineral content. Distilled water can be used in your fish tank for this reason as it has no minerals and is pH neutral..
The opposite is true for raising pH. Instead of removing minerals, you need to add minerals to act as a natural buffer.
What Is Aquarium KH
While talking about buffering and water hardness, I will briefly mention Carbonate Hardness (KH).
Carbonate hardness is the measure of carbonates (CO3), and bicarbonates (HCO3) found dissolved in water. A high KH acts as a good buffer against acid, which will eat away at the KH before it starts to affect your pH.
KH levels are not permanent and will gradually drop over time.
What Is The Difference Between KH And GH
KH (Carbonate Hardness) and GH (General Hardness) are often confused as they both refer to water hardness. Despite the similarity, the parameters measured are entirely different.
I have already mentioned that KH measures carbonates and bicarbonates. GH refers to the amount of magnesium and calcium dissolved in water. GH and KH are usually pretty similar in nature; however, a water source such as tap water can have a high GH and low KH.
When discussing tap water, people are usually referring to its GH. The hardness of aquarium water is more often referred to as its KH.
Important Points So Far
1. Lower pH water is better for soft water fish.
2. Higher pH is better for hard water fish.
3. Higher pH levels are more mineral-rich with a higher buffering capacity and more stability.
4. Lower pH levels are less stable and prone to sudden changes.
5. A high KH (Carbonate Hardness) is a good buffer against acid, preventing a downswing in your water’s pH.
How Does pH Affect Aquatic Life
Whether you own coldwater fish, tropical fish, freshwater fish, or saltwater water fish, they are all affected by pH levels. The natural pH in freshwater aquariums will usually differ slightly from the pH found in saltwater aquariums. The general pH of a freshwater aquarium will typically sit at 6.5 to 8.0 depending on the tap water used, while in a marine aquarium, the pH will be 7.9 to 8.5.
The pH level in a fish’s native environment results from natural minerals and other factors. If your aquarium’s pH is very different from what the fish are used, it can harm your fish. Very acidic water can cause burns to a fish’s skin, eyes, and lungs. Basic (alkaline) water can also cause these areas to become irritated (although not classed as burns).
Stress is another problem that can result from a pH value that is too high or low. Stress can lower a fish’s immunity and open them up to many illnesses that can be more serious than the initial skin irritation.
A combination of skin irritation and a lowered immunity can often lead to fatalities in your fish, so keeping a normal pH level is far more important than you may realize.
How Often Should You Test pH In An Aquarium
It is recommended that you test the pH in your aquarium at least once every 4-6 weeks. You may need to test in a newer tank more often until you find the natural baseline.
pH levels are generally a result of environmental impacts, so variations will usually be consistent. If your fish tank’s pH is swinging wildly up or down, this is unusual, and you need to identify the cause.
Generally speaking, pH is rarely a problem in most aquariums but can sometimes be affected by changes in water chemistry, such as ammonia spikes from a build-up of fish waste.
By tackling the cause of a pH change, it will often return to a normal level by itself.
To test aquarium water pH, you will either need to buy some relatively cheap test strips or an electronic tester that will be more expensive but provide more accurate readings and always be on hand.
When testing pH levels, keep a record for the first 4-6 months, and you may notice any patterns forming, which can help you predict future fluctuations.
How To Test pH In A Fish Tank
The 3 most accurate ways of testing the pH in a fish tank are by using A pH testing solution, pH test strips, or a digital meter.
Solutions and test strips are the cheapest options in the short term but they will need replacing from time to time. A digital meter is easier and quicker to use but will be more expensive in the short term, and will occasionally need calibrating.
pH Testing Solution Instructions
When using a solution, you will need to:
- Take a measured sample of water from the tank (usually into a test tube.)
- The instructions on the solution bottle will direct you to add several drops of solution to the sample.
- Mix the solution by gently shaking the test tube side to side and wait for the water to change color.
- Use the supplied color chart to find the matching color and pH value.
I have provided links below for the Saltwater and Freshwater solutions on Amazon and Chewy.com.
Although the Freshwater solution is often less expensive, both products are very similar and can be used for both water types. The main difference is the colors returned, which will be different, so you will need the correct color chart. I would suggest purchasing the correct kit for first use and keeping the color chart handy so that you can buy the cheaper kit in the future.
pH Test Strip Instructions
Test strips are much easier to use than a solution, and they are generally the cheapest option. To use a test strip, follow the below steps:
- Open the container and remove 1 test strip before closing the lid tightly to keep moisture from entering, and ruining the other test strips.
- Fully submerge the test strip into the tank water for a few seconds and then remove it.
- Wait for 30 to 60 seconds until the test strip has changed color and settled.
- Compare the color against the included color chart pH section to find the correct pH value.
Most test strips will give readings for all of the important parameters within an aquarium such as Ammonia, Nitrates, Nitrites, Carbonate Hardness (KH), General Hardness (GH), Chlorine, and pH, which is why you need to compare the correct area of the test strip to the correct area of the chart.
I use the Tetra Easystrips x100 test strips for freshwater and saltwater aquariums, and I will sometimes use the API 5 in 1 aquarium test strips x25 for freshwater and saltwater aquariums. (Affiliate links below)
Digital pH Meter Instructions
The last option (and the one that I now use most frequently) is the digital pH meter. These are the easiest and most convenient options, but they do need to be calibrated occasionally. Calibration is not difficult as you will only need to use a pH-neutral substance such as pure distilled water.
Another inconvenience is that most of these meters are only designed to measure the pH level, whereas the test strips and substances will give you the option to measure all important parameters.
Below are the correct steps to measure the pH of your aquarium with a digital meter:
- Ensure you have a good battery level.
- Remove the cap and ensure that the test head is clean and not contaminated.
- Turn on the meter.
- Dip the meter into your tank covering the test head fully.
- Remove the meter and wait for a digital reading of your fish tank’s pH level.
- Rinse the test head in clean water and replace the cap.
Yes, it is really that simple. These meters are all pretty accurate and they are not as expensive as you might think. Obviously the more money you spend on a meter, the better they are and the more features you will get.
Below are (affiliate) links to the meter I started with and the one that I use now. Both are good reliable meters.
Below is a video to demonstrate exactly how to perform each of the above tests.
Symptoms Of High pH In Fish Tank
There are several symptoms of high pH in a fish tank. A pH of 8.5 or higher is considered too high for most fish tanks and signals high levels of alkalinity.
Some of the most common symptoms of a high pH are:
- High levels of toxic ammonia – A ammonia build-up can be very toxic to fish, good bacteria, and plant life. Ammonia should not be confused with ammonium which is a symptom of a low pH. Ammonium is not considered toxic to fish.
- pH shock – pH shock typically occurs if pH changes suddenly. Symptoms may include general illness, loss of appetite, and sudden death.
- Fish seeming irritable – Twitchy fish jumping, scratching, shimmying, or just acting out of character can be caused by high pH. The skin irritation caused by excessive alkaline in the water can cause discomfort and, in worst cases, skin infections.
- Algae growth – Algae will thrive in alkaline-rich environments. Algae will thrive most at a pH between 8.2 and 8.7. Green algae are most common, causing green water, and also making your fish tank water cloudy, covering the glass until it is difficult to see your fish.
- Fish breathing at the surface – High pH can have a negative effect on oxygen levels in the water. A slight rise in pH can cause oligotrophic water (rich in dissolved oxygen) to become eutrophic (lacking in dissolved oxygen). This can cause your fish to swim at the top of the tank, where oxygen first dissolves into the water and is likely to be more abundant.
Symptoms Of Low pH In Fish Tank
Several symptoms may be present if your fish tank has a low pH level (higher acidity). Symptoms of low pH in a fish tank include:
- Fish may become pale, lethargic, inactive, and tired – When pH levels drop, it can have a negative effect on a fish’s metabolic rate. As a fish’s metabolic rate slows, cells can start to break down, and the body will literally be eating itself (a state known as autophagy).
- Fish may stop eating food as frequently – Again, caused by their metabolism slowing down, a fish will not need as much food to survive.
- pH shock – This can occur when the water’s pH drops suddenly, which can make your fish generally appear unwell and, in some cases, cause sudden death, especially with more severe pH swings.
How To Lower pH In Aquarium
There are several ways to lower pH in an aquarium, both manually and naturally, so let’s look at some of the manual ways first.
Use Reverse Osmosis
Reverse osmosis is a way to filter out minerals from the water by using a filtration device specifically designed to filter out microparticles. Using reverse osmosis, you are basically purifying the water, turning hard water into softer water, and removing the minerals that buffer the water by neutralizing acids.
Once your water has been softened, it will be more susceptible to a drop in pH, thus helping both a natural drop to occur or becoming more reactive when adding pH lowering chemicals.
The reverse osmosis process will usually create a more neutral pH level without any further intervention, although the equipment can be a little pricey.
Lower pH In Aquarium With Vinegar
Although it sounds strange, you can lower the pH in your tank with vinegar.
- The best method is to take a measured water sample from the tank and test it with a pH test kit. Once you have established the current pH of the water, you can add a small amount of white vinegar.
- As a rough guide, add approximately 1ml of vinegar per gallon of water. Mix the vinegar thoroughly and test the pH after 30-60 minutes.
- Once you have established the correct amount of vinegar to achieve the desired drop in pH, you can treat the rest of the aquarium water.
- Don’t add the vinegar directly to the tank as this can cause a sudden drop in pH and lead to pH shock; instead, remove and treat the water in stages, or just add the vinegar in stages (over 24 hours) until the total dose has been added.
Use API pH Down
A more simple method to lower pH is to add a commercially available chemical such as API pH Down, which will be available in most fish stores and is readily available to purchase online.
API pH Down is a nitrate-free, phosphate-free pH adjuster that will not cloud your tank or encourage algae growth.
Although pH Down is doing the same as white vinegar, you can be assured that the chemicals are completely harmless to your fish tank and will come with a comprehensive set of instructions.
How To Lower pH In Aquarium Naturally
Using the methods above will lower your pH level, but the results are not long-term. This is fine if you understand the cause of the fluctuation and can remove the cause. Still, if you are experiencing a permanently high pH, a more natural remedy may be a better solution and give more long-term results.
Peat Moss To Lower pH In Aquarium
Peat moss is a great way to lower the pH of your aquarium as it is naturally acidic and can be added beneath the substrate, out of sight.
The acidity of the peat moss will slowly dissolve into the water and eat away at any buffering chemicals until the pH begins to normalize and gradually soften your aquarium water.
Catappa Leaves (Indian Almond Leaves)
Catappa leaves (also known as Indian almond leaves) are from a tropical tree found in regions of Africa, Asia, and Australia.
I initially found out about the Catappa leaf when treating betta fish ailments, as it has many therapeutic and medicinal benefits to fish.
These leaves are rich in tannins which will turn your tank water a shade of brown, but they are wonderful for regulating the pH levels in your aquarium.
Driftwood is another natural method of lowering pH because, like Catappa leaves, it also contains pH-lowering tannins.
It is essential to use natural driftwood with the highest tannins level without added chemicals.
Do Live Plants Lower The pH Of Aquarium Water
Live plants don’t lower the pH of an aquarium, they increase the pH level. During the daytime, live plants absorb carbon dioxide to produce oxygen. Carbon dioxide helps lower the pH of aquarium water, while oxygen has no effect on water pH.
If you have an overgrowth of plants, try removing some of them. Just a slight reduction of plants will help lower the oxygen content in the water, making room for some acidic carbon dioxide to lower the pH level.
Finding the right balance will make your tank look good, are essential to the diet of many fish species, and provide a good balance between oxygen and carbon dioxide.
Live plants are great for aquariums, and with regular care and cleaning, they will help with many natural functions within the tank, leading to a healthy, oxygen-rich, bioactive environment.
Add Carbon Dioxide
Although you can add carbon dioxide manually to a fish tank, there are more natural ways, such as adding organic matter, which will release carbon dioxide as it decays.
Allowing organic matter to decay is a safe process that will happen over time, having a more stable and long-term effect.
When in water, carbon dioxide will act as an acid, which will help normalize the level of alkaline over time.
It is possible to add carbon dioxide manually; however, the effect would be more sudden, potentially harming your fish.
How To Raise pH In Aquarium
Understanding how to raise your aquarium water pH is just as important as lowering it, so let’s look at raising it manually first.
Regular water changes are the easiest way to keep your pH level stable. Most tap water will contain minerals that will help buffer up your pH.
You should always check the pH of the tap water in your area before adding it to your tank. It is important to know the chemical makeup of the tap water you are using so that you can treat it correctly and match it to the type of fish you have.
Aerating The Water
Adding dissolved oxygen to your aquarium through aeration does not directly impact pH; instead, it will reduce the level of acidic carbon dioxide, enabling the pH level to rise.
Aeration can be achieved by surface water disturbance such as a good filter flow rate at the top of the tank, or just stirring/splashing the surface water.
How To Raise pH In Fish Tank With Baking Soda
Baking soda is very alkaline and can raise the pH quite quickly. With any method that causes a quick change in the pH of your aquarium water, you will need to either do it in stages or remove your fish to a separate holding tank until completed.
The best method to follow when using baking soda to raise pH is:
- Take a small water sample (this can be 1-10 gallons, dependent on your tank size).
- Test the water with pH test strips before adding any baking soda. This way you can gauge how quickly it changes.
- Add the baking soda to the water sample. 1 teaspoon of baking soda per 5 gallons will usually raise the pH level by around 1 point if it isn’t too far from neutral.
- Stir the baking soda into the water allowing it to dissolve, and sit for 30 minutes before re-testing. Take note of how much the pH rises.
- If you are going to remove your fish from the main tank, you can add some of the sample water into a holding tank, mixing some of the main tank water with it. If the pH rises too quickly your fish may suffer from pH shock, so you want to avoid this.
- Treat the rest of the main tank water with baking soda using the same ratios used on the sample water.
- Once your main tank has reached the correct pH, you will need to gradually mix small quantities into the holding tank (for 12-24 hours) so that your fish get used to the change.
- Add your fish back to the main tank.
I have suggested removing your fish to a holding tank, although this may not be necessary for minor changes such as from 6.5-7.5; however, larger changes of around 6 to 8.5 or from 9 to 7 are generally larger than most fish can tolerate without showing signs of stress.
If you only require small adjustments to your aquarium’s pH, it may be better to use some of the more natural methods which will happen over time and be a more permanent solution.
Reverse osmosis will not only lower pH but will also raise pH. Because this method has the effect of purifying water, the result is a more neutral pH value.
Api pH Up
The opposite of the API pH Down formula above, this will slowly neutralize the acid in your fish tank without any harmful phosphates or other chemicals, and it doesn’t promote algae growth like some other methods.
How To Raise pH In Aquarium Naturally
Natural changes are often best because they are more permanent and gradually affect water chemistry. Water remains relatively stable in a fish’s natural habitat because of many environmental factors such as water’s mineral content and oxygen content.
Here are a few ways to naturally raise the pH in your aquarium.
Add Live Plants
Plants are the perfect, natural source of oxygen, and they have many other benefits in creating a bioactive environment. As mentioned above, carbon dioxide is acidic in water, and aerating your fish tank will combat this problem. Live plants will naturally remove carbon dioxide from the water while adding oxygen.
Add Crushed Coral Or Dolomite Gravel
Adding minerals such as those in crushed coral or dolomite gravel will create a buffer that protects against acidity, allowing the pH to rise. You can add these substances directly to the substrate in your tank for a slow increase in mineral levels, or you can put them in a netted media bag (available on Chewy.com and Amazon) and place them within the filter element. This way, the minerals will be distributed more quickly through your aquarium.
Using crushed coral or dolomite is a long-term buffer that will help create a more stable pH environment.
Use Limestone Or Coral Rock For Decoration
Limestone or coral rocks will act the same way as the crushed coral or dolomite mentioned above. They are both mineral-rich and will create a buffer to absorb excess acid from the water.
You can purchase ornaments and features made explicitly from limestone or coral rock which you can use to decorate your tank and act as a permanent pH buffer.
Many people use driftwood as decoration in their tank without realizing that the natural tannins released are acidic, lowering the water’s pH value. If you are struggling with a low pH, simply removing some or all driftwood from the aquarium, you should see an improvement.
Changes to pH will be gradual when adding or removing mineral-rich objects because minerals take time to dissolve into and away from the water. Natural buffers will take even longer to take effect in larger tanks, but creating a stable, balanced environment is worth the wait.
Water pH can be a very confusing topic, especially when looking at it from a scientific point of view. There are many conflicting terms such as General Hardness (GH) and Carbonate Hardness (KH), or Alkaline and Basic, which both refer to Alkaline but in different situations.
I am by no means an expert on water pH, and I have only ever researched as far as is necessary, so don’t be disillusioned if you have reached this far and are still confused.
As far as fish keeping is concerned, you only need to understand how to measure pH, why it can increase or decrease, and learn some methods to raise or lower your pH quickly or naturally and over time. If you want to understand more about hydrogen ions and hydroxide ions, that’s up to you.
Water chemistry can become far more complicated than it needs to be and if I were to try and explain everything there is to know on the subject, this article could quickly turn into a book.
Problematic pH levels are not that common, and a well-set-up tank that is cleaned frequently has good filtration, is not overstocked, and should have a naturally stable pH.
Many people believe that aquarium fish need to live in a specific water type and bang their heads against a wall trying to achieve this perfect value. Yes, some fish are better suited to particular water, but most fish will adapt if your pH is neutral and stable.
I explained that each point on the pH scale results in a 10x multiple of the previous value, which is a crucial fact to note, so the further you are away from neutral in either direction, the more severe each 1 point movement will become. For example: A change from a pH value of 9 to 10 is far more severe than a pH change from 7 to 8. The pH increase from 7 to 8 is 10x as much alkaline, from 8 to 9 is 100x more alkaline, and 9 to 10 is 1000x more alkaline.
You should initially test your fish tank’s pH regularly and don’t allow your pH values to increase or decrease by more than 1-1.5 points. Most freshwater fish tanks will do just fine within the range of 6.5 and 8. Water that is slightly more alkaline is safer and more stable than a lower acidic level.
Cycle a new aquarium properly before adding fish and try not to make any sudden changes to the water chemistry. All water parameter changes should be slow and steady, so they don’t impact negatively on your fish’s health.
I hope this article has been helpful in explaining the important aspects of pH levels, and what role they play. You have done very well if you managed to reach the end of the article without falling asleep.
Try not to become obsessive about pH levels, and instead treat it as just one piece of the puzzle when it comes to your fish tank’s water parameters. There are many, far more important things that can throw your water parameters into disarray, and most of them can be avoided by having a regular schedule for cleaning, and basic fish tank maintenance.