Everything you should know about Aquarium pH

Everything you should know about Aquarium pH

When we talk about the requirements of freshwater aquarium fish, pH holds an important place. Have you ever wondered why we always talk about maintaining the right aquarium pH when fish, by default, are wild in nature and easily survive in rivers?

Every pet has its own set of requirements, but when it comes to fish, some additional efforts are required to keep them alive. Water quality decides the survival of fish. If there is a mismatch in any of the water parameters or if they are not in range, fish may get sick and eventually die. Out of so many water parameters that we need to ponder, aquarium pH is something that we cannot neglect.

Every fish has its own tolerance to pH. It is possible that a pH range suitable for fish A is likely to kill fish B. Therefore, it also becomes an essential criterion while deciding the fish you want to keep in your aquarium. However, the good news is, other than a few expectations, the survival of most fish falls within the same pH range. So you can pet most of them together.

In this article, we will discuss the most common questions regarding pH that new aquarists often ask. Also, we will provide a guide on how to lower down and raise the aquarium pH whenever required.

What is pH?

pH stands for potential of hydrogen ion, which means it measures the concentration of hydrogen ions in water. Danish botanist Søren Peter Lauritz Sørensen devised the pH scale.

If you do not want to go into detail, pH can be simply understood as the basis of water chemistry. pH in an aquarium depends upon a number of factors like:

  • The concentration of chemicals in the tank that may build up with fish excreta, waste food, etc.
  • Type of substrate you are using in your aquarium setup
  • The amount of trace minerals present in the tank

What is the pH scale, and how it determines water quality?

The pH scale ranges from 0 to 14, that help in determining the water’s condition. As per the scale, if the pH is 7.0, it is neutral. If the reading comes below 7.0, it falls under acidic and above 7.0 is basic.

As per the chemistry, when you test the water with a pH scale, and the reading comes below 7.0, it signifies soft water or acidic water. Similarly, when the pH of water is more than 7.0, it is alkaline or basic water. Water with pH 7.0 is neutral.


How do different pH levels affect different fish?

Every creature that lives in water, including plants, have different pH tolerance. Therefore, when you plan to have both- fish and live plants in the tank, you have to make a thoughtful choice. For instance, certain fish and plant species accept high alkalinity levels; others may collapse in the same water conditions. Thorough research and complete knowledge of fish and plants is a prerequisite when you are choosing tank mates.

If the pH goes up or down from the range, the chances of fish getting sick, stressed and dying are very high.

What is the effect of different pH levels on water chemistry? 

When it is about water chemistry, pH is the major contributing factor. At the same time, pH can also impact other elements of water quality in the aquarium. Let’s find out how:

  • pH below 6.0– If the level of pH drops below 6.0 in the aquarium, a few beneficial bacteria that can eliminate nitrites, ammonia and other toxic elements from the water start dying. As a result of the high level of ammonia, fish species that cannot tolerate it begin to die off. In a nutshell, ammonia toxicity increases when the pH is below 6.0 in a tank for a longer period.
  • pH above 8.0– If the level of pH rises above 8.0 in the aquarium, you will start noticing sudden changes. For instance, the growth of green algae on the walls and on the ornaments in the tank will rise. High pH favours the growth of algae and slimes that coat thickly on the plants and fixtures and decrease the aesthetic of the tank. Also, it makes water highly toxic for fish.

How pH and Ammonia are related?

Ammonium compounds that are ammonia (NH3) and ammonium ions (NH4+) decide the ammonia levels in the water. Ammonia levels, in turn, decide the pH of the water. So, if the aquarium water has a higher concentration of ammonia, pH will be in the higher range, i.e., more than 7.0. Similarly, if the concentration of ammonium ions in the water is higher, the pH will be below 7.0, and the water will be called acidic.

Out of these two ammonium compounds, ammonia is most dangerous to the fish. 

So, if, in anyways, the pH of the water rises, the water becomes toxic for the fish. Therefore, it is advised never to mess with the aquarium water pH, especially when you are cycling a new tank. There should be no ammonia once the tank has finished cycling. In this way, the water gets adjusted to pH safely.

What is the pH of tap water? Is it safe to use in the aquarium?

Generally, aquarists use tap water only for their aquarium. The pH of tap water is not constant but varies depending on where you live. While most of the tap water pH falls under a suitable pH range but it is necessary to find out whether the domestic water supply is suitable for your aquarium or not.

How to find the pH of tap water?

The best way to find the pH of your tap water is by following the steps below:

  • Fill a bucket with tap water
  • With an air stone, oxygenate the water
  • Let the water rest with the air stone for at least 24 hours
  • Take out the pH reading scale and note the reading
  • Take another reading after the next 24 hours. This will be the correct pH reading of your tap water.

What is the need of resting the water for 24 hours?

Allowing water to rest for 24 to 48 hours helps to get an accurate reading. It is because the pH level drops down due to the carbon dioxide level in the water. When you agitate the water surface with an air stone, oxygen is pulled from the air into the water. This, in turn, drives excess carbon dioxide from the water into the air.

When the carbon dioxide levels drop down, the water pushes up the pH level. It is the reason why taking the reading after resting the water for at least 24 hours will give the accurate one. Oxygen and carbon dioxide exchange in water is a constant process, so there is no other way of taking the precise pH reading of tap water. The presence of chemicals and décor items in the tank also influences the pH.

What is kH, and how it is related to pH?

The concentration of bicarbonate and carbonate ions in the water refers to kH value. In another way, one can understand kH as a barometer providing the ability of water to neutralize or buffer acids without altering the pH. Apart from pH, kH is another critical element that you need to check out in your aquarium as it is related to the acid content in the water.

The more is the kH level in the aquarium; the more stable the pH level would be. On the contrary, if the kH is too low, the pH will vary dramatically. You can easily observe swings in the water chemistry if the kH value is below 4.5 dH.

To avoid it, conducting water changes regularly is the right thing because kH value drops down with time. Therefore, it is always advised to practice water changes weekly as it will help in maintaining the kH and pH value of the water and keep everything under tolerable range.

What should be the pH level in a freshwater aquarium?

Generally, most of the freshwater fish species survive well between the pH range of 6.8 and 7.6, which implies that the acidic content in water is neither very high nor extremely low. 7.0 is the neutral pH level. Still, it is suggested to research a bit more about the specific pH requirement of individual fish and plant species you are planning to have in your tank. It will ensure that your fish will survive and won’t fall sick due to poor water quality.

What is an aquarium water kit?

The Aquarium water kit is one of the essential aquarium products that every aquarist must-have. With the help of an aquarium water kit, you can check the different water parameters, including pH. You can buy it from the local pet shop or online, but make sure of buying a reliable and quality kit for getting the right reading.

Aquarium test kits are available in two forms-

  • Dip strips
  • Solution form

Both of these kits work in the same way and provide the reading. Basically, what you have to do is comparing the reading of your sample with a colour chart that comes with the kit. The colour of the sample you get indicates the pH and kH level in the aquarium water.

There are a few downsides to using the aquarium water testing kits. These are:

  • Sometimes the readings do not come accurate, and you end up getting a false one.
  • Most of the kits expire in six months, so they have less shelf life. If you use an expired kit, you will get incorrect readings.

It is generally recommended to take the reading twice as it will double sure that you are getting it right. You should follow the instructions written in the user manual very carefully to know the procedure of doing the test on your sample.

What if the pH is not within the range?

In case you are getting pH higher or lower than the desired, you have to alter it in different ways. Also, you need to do it with an immediate effect to avoid getting your fish under stress. Here are the ways you can alter the pH:

Different ways to raise the pH levels in the aquarium

If there is a serious drop in the pH level, it means that water has gone highly acidic. As previously mentioned, it can create havoc in the life of your aquarium creatures. But the good news is you can adjust it in different ways and correct the problem. Check out how to raise the pH levels in the aquarium.

  1. Through water aeration 

You can increase the pH level of water through aeration, which can be done by increasing the amount of dissolved oxygen. When the amount of oxygen increases, the concentration of carbon dioxide reduces. Since carbon dioxide is acidic and produces carbonic acid in dissolved form, its lesser concentration will turn the water basic, and subsequently, the pH will rise.

Now the question is how to oxygenate the water? There are different ways through which you can oxygenate water like:

  • By agitating the water– It can be done by putting the aquarium filter outlet above the water surface. It aids in the movement of oxygen into the water from the air above the water.
  • By using an air pump– You can use an air pump or powerhead that agitates the water and increase the flow within the aquarium. Apart from increasing the flow, it also moves the air into the water. If you are using an air pump or powerhead, make sure that fish in the tank are tolerant to strong currents.
  • By water changes– Regular water changes will maintain the water quality by maintaining good dissolved oxygen levels and less concentration of carbon dioxide.


  1. Through partial water changes 

pH alters due to a variety of reasons, out of which fish excreta is one major contributing factor. When the fish waste starts accumulating, the concentration of chemicals rises that drops the pH level drastically. To raise the pH level, you need to reduce the fish excreta and all the pollutants that are increasing the chemical concentration.

Most of the pollutants reside at the bottom of the tank- at the substrate. You can clean the aquarium substrate by cleaning through vacuuming every week. Also, avoiding overfeeding the fish is a good way to keep pollutants minimum.

Partial water changes or replacing around 20% water every week helps in reducing the chemical concentration. Replace aquarium water with dechlorinated tap water to get rid of excess pollutants from your fish tank.


  1. Through Baking Soda

If the pH level has dropped down drastically, adding a small amount of baking soda will also help. The only thing to keep in mind while using this method is to continue adding baking soda after every few hours to maintain the results; otherwise, the pH will fall back to its original level.

For every 5 gallons of water, one teaspoon of baking soda will suffice to raise the pH level. Just make sure you do it slowly, or else the fish will get shocked and come under stress. Other than baking soda, you can also add chemicals like sodium bicarbonate. Reapply the chemicals regularly to keep the levels stable.


  1. By changing the aquarium substrate 

Gravel can decide the pH of your tank. For instance, using calcium carbonate gravels can significantly alter the pH of your tank. Some of the most effective carbonate-based gravels include the following:

  • Limestone
  • Crushed charcoal, which is calcium carbonate gravel pieces
  • Petrified coral rock
  • Specific types of shells

Once you have changed the substrate, it is advised to regularly check the pH with an aquarium testing kit and keep an eye on water parameters. It is because such substrate may raise the pH more than what you actually desire. Another way is to place the materials in the filter unit to avoid the spike in pH level in the aquarium.


  1. By soaking driftwood 

Often aquarists use driftwoods as an aquarium décor, lesser knowing the fact that they leach tannins and tannic acid that drop down the pH in the aquarium. It gets hard for the new aquarists to find out the reason behind low pH when every other thing is fine. In such cases, driftwood could be a possible reason.


So if you are into aquarium décor and love to put driftwood but find it highly frustrating to see low pH levels all the time, switch to natural wood with resin decorations. It will mimic wood and look cool. However, if you are a diehard fan of driftwood and don’t want to try natural wood, boil it before placing it in the aquarium. Boiling the driftwood will remove the tannins and make it safer for the fish.


Different ways to lower the pH of the tank

In case the pH of the tank has increased more than the desired range, you can decrease it easily in any of the following ways:

  1. By using certain chemical solutions 

A bottle of chemical solution is helpful in maintaining the water pH as per the specified range. You may find different products in the market labelled as ‘water softener’, ‘pH reducer’, pH lower’ and a lot more. Using these bottles can help in lowering the water pH.

While most of the products have diluted acids as an active ingredient, some use natural methods like organic matter and tannins for solving the purpose. Make sure you use them as per the directions written on the label for the best results.


  1. By using driftwood

One of the best and natural ways of lowering the pH is using driftwood. Using driftwood is a cakewalk. You don’t have to put in any extra effort or skills or follow special instructions. All you need is to place driftwood in the aquarium, and it will lower the pH. At the same time, it will also be helpful in the following ways:

  • Add to the aesthetics of the tank
  • Provides cover for the fish and invertebrates in the tank
  • Creates tea-coloured water to create rainforest river-style aquarium
  • Helps in aquascaping


  1. By using Peat Moss

Another easy way to lower the pH is using peat moss which is a lot higher in tannins than driftwood. However, one downside is it makes the water tea-coloured if you use it in more quantity. So, if you prefer crystal clear water, leave this option entirely.

Peat Moss is often used with the substrate, especially in a planted aquarium. It buffers the pH towards acidity and helps in releasing the organic matter directly to the plant roots after decaying. So, if you plan to add peat moss, do it before adding your fish in the tank so that the water chemistry can be adjusted as per the requirement of the fish.


  1. By changing water 

Just like water changes or partial water changes helps in reducing water’s acidity, it can also help in reducing the water’s alkalinity. Most of the time, the high level of pH is due to elevated ammonia. It often occurs due to fish excreta and leftover food. Therefore, if you want to stabilize your tank pH, practising regular water changes will definitely give good results and keep your tank clean.


  1. Through Reverse Osmosis Units 

If your tap water is mineral-rich, you may need to invest in a reverse osmosis unit. The process of reverse osmosis eliminates ions and molecules from the water that not only makes the water clean but also increases the alkalinity. RO membrane allows only small ions to pass through it. The heavy ions that are harmful to the fish are removed.

The only downside of using an RO unit is you have to replace the filter from time to time. This method is appropriate, particularly if you are using hard water.


  1. By decreasing aeration 

Another proven way of lowering the pH is decreasing the oxygen level in the tank. When the level of oxygen decreases, the level of carbon dioxide increases that subsequently results in lowering the level of pH.

Although the method of decreasing aeration in order to lower down the pH is cost-effective and easy, you have to be extra cautious while doing so. It is because fish require oxygen for surviving. If the quantity of dissolved become too low, it will become difficult for the fish to breathe, and they may come under stress.


Final words

Aquarium pH is one of the factors that determine the happiness of the fish. Therefore, in order to keep your adorable pet fish happy, healthy and thriving, having the right pH range in the tank is essential.

If you are facing troubles in maintaining the right pH, you can use any of the above methods to increase or decrease it. All you need is to ensure that water has the right pH and it is stable. It is because fluctuations may cause stress in fish and can be fatal.

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