PH (Potential Hydrogen) measures the acidity in a solution or substance. This measure ranges from 0 to 14, with 7 as the neutral mark. A substance with a pH value between 0 and 6.9 is acidic. A pH between 7.1 and 14 is termed alkaline.

The symptoms of high pH levels in a fish tank include algae growth, high levels of toxic ammonia, pH shock, and irritable fish. Irritability in fish includes shimmying, scratching, breathing at the surface, and gasping. Reduce high pH by adding wood, CO2, and peat moss, or reverse osmosis.

Most fish thriving in fish tanks are freshwater fish where such water has a neutral pH. Too acidic or alkaline water in a fish habitat can threaten your fish’s health. Thus, it is considerably mindful to check such signs before they bring problems to your aquatic creatures.

What is the Optimal pH for a Fish Tank?

Different species of fish survive in different pH values. Since most aquarists keep many fish species in the same aquarium, finding a pH level where all fish live comfortably would be best. 

For instance, most freshwater tropical fish perform best between pH values of 6.8 to 7.8. However, quite a few species come from areas with slightly lower or higher PH values. 

Cichlids, for example, are fish in the Rift Lakes of Africa that have adapted to living at high pH values in an aquarium between 8.0 and 9.0. On the other hand, Cardio tetras from the Rio Negro of South America survive in water with a pH below 5.5. 

Most aquarium fish in today’s market are captively bred within different pH values from their natural environment. Thus, adapting the fish to your water tank is important since most have never been there. 

How to Check the PH of a Fish Tank

There are 3 common and accurate methods of testing PH in a fish tank. These include using pH test strips, a pH testing solution, and a digital meter.

Testing strips and the pH solution are considered the most affordable options in the short term but require frequent replacement. 

On the other hand, a digital meter is considerably quicker and easier but can be more expensive in a short time, necessitating occasional calibration.

Test your water’s pH when a fish gets sick or when there are any chemical changes. Other than that, a weekly pH check is okay.

1. PH Test Strips 

Compared to pH solutions, pH test strips are easy to use and generally the cheapest choice. Here are  the steps you follow when testing pH in a fish tank using a test strip:

  1. Clean and dry your hands then open the test strip container, remove one strip, and close the lid tightly. This prevents moisture from the air from damaging the other strips.
  2. Submerge the test strip fully into the fish tank for a few seconds, then remove it.
  3. Allow about 30 to 60 seconds for the test strip to change its color and maintain its new color.
  4. Use the pH chart to match the color of the PH test strip with the matching PH value on a fish tank pH level chart like the one below.

Most test strips will provide readings of all essential parameters within a fish tank. This may include Nitrates, Ammonia, Carbonate Hardness (KH), Chlorine, General Hardness (GH), and PH. Ensure you match the test strip to the correct area of the chart.

2. PH Testing Solutions

Here are the steps you follow when testing pH in your fish tank using pH solutions:

  1. Collect water samples from the fish tank, preferably into a test tube.
  2. Add a few drops of the pH testing solutions to the water sample according to the prescribed instructions on its container.
  3. Mix the mixture intensively by shaking the test tube in different directions until the water changes its color.
  4. Use the issued color chart to identify the matching color to the pH value.

For the best results, buy the best kit for the first attempt and secure the color chart at hand to allow you to buy cheaper equipment for subsequent tests.

3. PH Digital Meter

Our final option is using a pH digital meter to identify the pH of your fish tank. This is the easiest and most reliable option but requires occasional calibration. However, calibration is not difficult as you will only need a substance with a neutral PH value, such as distilled water. 

Also, this digital meter only shows the pH level, unlike the solution and test strips which will measure the pH value alongside other essential parameters. 

Below are the steps for testing the PH level in your fish tank using a digital meter:

  1. Ensure the meter’s battery has the correct level of charge.
  2. Remove its cap and ensure the test head is clean and sterile.
  3. Switch on the meter.
  4. Drop the meter into your tank and fully submerge the test head.
  5. Withdraw the meter and wait for the digital pH reading that will show the pH level of your fish tank.
  6. Using clean water, rinse the meter’s head and cover it using its lid.

It’s that simple. These meters are quite affordable and less expensive than other methods. 

Symptoms of High PH in a Fish Tank

There are several symptoms of high pH in a fish tank. A pH level above 8.5 can be considered too high for most fish tanks and shows a high alkalinity level.

Here are some common symptoms of a high pH in your fish tank:

  • PH shock is caused by a sudden change in the pH level. It can be evident from various signs such as sudden death, loss of appetite, and general illness in fish or other aquarium pets.
  • High levels of toxic ammonia: High ammonia accumulation can be toxic to fish, plants, and bacteria. This should not be confused with ammonium which is a low pH level. Ammonium is considered non-toxic to fish.
  • Fish behaving irritably: High pH can cause the fish to have alkalosis (illness caused by high pH) and behave by shimmying, scratching, and other awkward characteristics. Excessive alkalinity in the water can cause skin infections and discomfort to fish.
  • Algae growth: Algae flourishes in very alkaline environments between pH 8.2 and 8.7. Typically, green algae will grow, turning your water covered with a glass or appearing cloudy, making it difficult to see the fish.

Any one or a combination of these signs can point to the fish tank being too alkaline. You can easily test it to find out how much.

What Causes High PH in a Fish Tank?

Here are the most common causes of high pH in a fish tank:

1. Tap Water

Tap water contains metals and alkaline compounds. This is among the key reasons why most aquarists advise against using regular unconditioned tank water in your fish tank. 

2. Ineffective Filters

Old or ineffective filters can be destructive in various ways. For example, they drive the water pH to be unpleasant to fish. Broken organic materials and fish waste increase the pH level.

3. Aquatic Plants

Aquatic plants like water lettuce in a fish tank can trap minerals such as nitrates and carbon dioxide, sliming on decorations, glass, and rocks. This implies that the pH level is extremely high, which is unpleasant to most fish.

4. Stones and Rocks

Some rocks and stones can increase your water’s pH level. For instance, materials with high calcium levels, such as limestone, can mix and dissolve into the water, increasing the PH level.

Similarly, you can add crushed stones and shells at the bottom of your fish tank to increase the pH levels.

Symptoms of Low PH in a Fish Tank

Multiple symptoms in your fish tank can demonstrate a higher acidity (low pH level). They include the following:

  • PH shock can be caused by a sudden drop in the pH level in your fish tank. This makes your fish behave abnormally, causing illnesses and sudden death due to high pH variations.
  • Loss of appetite in fish: A low pH will lower the fish’s metabolic activity, requiring little food for survival.
  • Fish may appear inactive, pale, tired, and lethargic: A low pH level in your fish tank will harm your fish’s metabolic activity. The fish’s metabolism slows, making the cells start breaking down, and the body literally eats itself.

Low pH in the fish tank is actually more dangerous than high pH hence the need for a quick remedy.

What Causes Low PH in a Fish Tank?

Low pH is caused by the following:

  • Inadequate aquatic plants
  • Excess fish
  • Dead and decaying fish
  • Overfeeding
  • Sick or contaminated fish
  • Substrate/ aquarium hiding waste
  • A dirty tank
  • Variation  of water sources

These are causes that you can easily observe in your routine fish tank checkups.

How to Change the PH of a Fish Tank

You can effectively raise or lower the pH level in your fish tank using the following methods:

Raise fish tank pHLower fish tank pH
Water changesAdding wood
Adding substrates and rocksAdding filtering peat moss
Baking sodaReverse osmosis
Increasing oxygen levelsIncreasing carbon dioxide levels
Adding chemicals

How to Raise PH Levels in a Fish Tank

Low pH in your fish tank can be unfavorable to your fish’s health. Here is how to raise the pH levels in your fish tank:

  1. Water changes: You can moderate the pH level in your fish tank by performing routine water changes. This can be achieved by topping up with a water conditioner and tap water. Water change is easy in a bowl for fish types that can live in a fish bowl given the bowl’s size.
  2. Adding substrates and rocks: Some rocks and substrates are good for controlling the pH level in your fish tank. For instance, crushed coral can be a perfect choice for increasing the pH level in your aquarium.
  3. Home remedies: Baking soda is a common useful home remedy for controlling the pH in your fish tank. You can easily manage low pH by adding baking soda to your fish tank.
  4. Increasing oxygen levels: Supplying oxygen in your fish tank lowers the carbon (IV) oxide concentration. This, in turn, raises the PH to the appropriate level suitable for your aquatic creatures.
  5. Adding chemicals: Although not an effective method, you can add commercial buffers in your fish tank as a temporary solution for low pH.

Always start by checking the pH level of your fish tank then decide how much of the options above you need. With plants such as cucumber in fish tanks, always be sure of the plant’s effect on the pH before adding it to the tank.

How to Lower PH levels in a Fish Tank

Lowering the pH level in your fish tank can seem more challenging than increasing it. Fortunately, you can easily achieve this by:

  • Adding wood: Wood such as driftwood leaches tannins that can lower the pH level of water in your fish tank. Also, it can be good to add extra hiding places and areas for fish to hide in your tank.
  • Filtering peat moss: You can add peat moss in a mesh bag or substrate in your fish tank. However, water may later discolor and clear up.
  • Increasing carbon dioxide levels and adding reverse osmosis (RO) in water: You can pump or increase carbon dioxide levels by adding plants or RO in water, which are effective ways to reduce pH levels in your fish tank easily.

Be careful when lowering the pH of your fish tank since overdoing it can kill your fish.

Bottom Line

Getting the right pH levels in your fish tank ensures your fish stay healthy and thrive. Luckily, you can easily identify high and low pH symptoms in your fish tank and take appropriate actions. Moderate the pH level in your fish tank with the methods above.


Duke University. What do you need to know about water chemistry and why?

Southern Regional Aquaculture Center. Managing High pH in Freshwater Ponds.

Kentucky State University. Pond pH and Ammonia Toxicity.

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