Aquaforest / Blog / Articles / How to lower pH in aquarium & what causes high pH in fish tank?

How to lower pH in aquarium & what causes high pH in fish tank?

19 06, 2023









High pH in fish tank - when it is problem?

The pH scale ranges 0-14:

  •  If water has a pH lower than 7, it is acid.
  •  If water has a pH higher than 7, it is alkaline.
  •  PH of 7.0 is neutral.

High pH level of water start being trouble when it exceeds healthy limits for fish and other creatures living in the tank. Correctly pH range will be different in every aquarium, everything depends on a cast in your tank.

Dangers of high pH in an aquarium may cause plenty of problems, like increased stress, diseases (alkaline diseases), and even death. That is why you should often test the pH in your aquarium, watch it, control water quality, and act quickly if needed. 

What causes high pH in aquarium?

Aquarium pH issues is a common case in the aquarium hobby and depends on many factors. It's hard to pinpoint the cause of the change in the pH. Luckily, science and our knowledge about aquariums is still developing, and now, we can already show you ways to lower, and causes of raising the pH.

There are a few common causes of high pH in an aquarium:

1. Decoration elements

Decoration elements with a high calcium content, like stones, rocks, and seashells, will change the pH of the water. The first step is: remove them off from the tank and observe changes.

2. Hard Water

If you use tap water, it may be too hard, meaning it contains high levels of minerals such as calcium or magnesium. You may want to consider starting with AF Water Conditioner. This is our product designed to treat tap water with added vitamins and a protective colloid. Instantly, it prepares tap water for direct use in aquariums. Furthermore, it reduces chlorine levels, which are a danger to fish.

3. Too many plants

Plants in an aquarium do not change the pH level unless there are too many of them. During photosynthesis, they give off a lot of carbon dioxide, which acidifies the aquarium water. It is then best to remove some of the plants. Then, as with the decorative elements - monitor the pH.

4. PH raising substrate

Usually, substrates are sources with a neutral pH. However, when you are using sand or gravel, you need to check what is it made of. Some types can increase in pH and hardness of the water, e.g. aragonite sand.

We recommended using ready-made substrates like AF Natural Substrate. It is the perfect choice for freshwater aquariums. A fertile, nature-like environment is created by readily available micronutrients and plant food within it. This is ideal for long-time plant support and growth. Moreover, this product will acidic water and releases essential minerals into the water. 



Ways to reduce pH in aquarium

First of all, you need to check the pH level in the tank. There are a few ways to test pH: using liquid tests or strip ones, digital pH meter.

If you are past this stage and your water pH level is higher than that needed by the animals living in the tank. Don't be scared, their safety, well-being and growth are important to us. We have some solutions to lower the pH.

The best ways to adjust pH are natural solutions. Using chemical products is effective, but this way requires a lot of responsibility and precision. If you decided on this solution, we recommend following the instructions on the labels so as not to harm aquarium life.

If you want low pH water, take a look at this solution:

1. Water changes

Start there. This is the easiest solution to safely lower pH of water. This way will help, only provided that the water you intend to add to the tank has a more acidic reaction than the water in the tank.

2. Peat moss

Next one, very safety and natural solution to adjust the pH is adding peat moss to the aquarium. It will release tannic acid and gallic acid, tannins that lower pH. These acids will take care of the bicarbonates, leading to a reducing of the pH and hardness.

Start by adding a small amount of peat moss to the aquarium and continuously checking the pH. Add more if you do not notice a change in pH. Remember that for this method to work, the peat must remain in the filter. 

Unfortunately, this solution has one disadvantage. When moss is added, the water will change colour, but not for long. Many people enjoy this effect.

3. Driftwood

There are many types of wood and roots that are used in an aquarium. The most popular of them: Manzanita, Mopani, Red Moor Wood, Opuva, Winewood.

This is one of the most effective ways to lower pH in your aquarium. Moreover, thanks to driftwood, freshwater fish will not be exposed to stress because this solution makes changes slowly.

As with the previous method, it is very possible that the water will change the color. Don't worry, this is a natural process, that will not harm your fish.

4. Indian almond (Terminalia catappa)

The leaves of the Indian almond are what we are interested in. These leaves help lower pH in the aquarium and also have antibacterial properties. This has a positive effect on the fish's resistance. The next advantage of this solution is a substrate, which will be created by leaves on the bottom of the aquarium. This is a place where many fish like to forage or hide.
Alder cones or oak leaves are good alternatives for Indian almond.

5. Reverse osmosis (RO)

Also known as the deionisation process. This process produces water that is almost completely purified of impurities and minerals. The membrane filter helps to maintain the optimal pH of 7, which means it's completely neutral.

This ensures that aquarists do not have the problem of water discolouration. It is worth knowing that filtration in this way also helps to lower kH and gH levels.

The biggest disadvantage of this solution is the price. It is one of the most effective ways to lower pH level, but also one of the most expensive.

  1. CO2 Reactors

This is a solution which great works in aquariums with many plants. Carbon dioxide is essential for plants to carry out photosynthesis and grow healthily. Additionally, CO2 has acid reaction, so it gets the pH lower.

If you have decided to buy CO2 reactors, you should also think about buying CO2 and oxygen sensors. It helps to maintain the correct value of these parameters in the aquarium.

7. Chemicals

This solution should only be used as a last option. It is always better to find natural ways to lower the pH.

As we mentioned earlier. Using aquarium chemicals can change the pH, but it is more complicated than it sounds. Often, but not always, chemicals do not remove source of the problems, they only temporarily reduce the pH.

The big advantages of using chemicals is that they start working immediately. 

How to lower pH in aquarium quickly - is it possible?

The quickly lower the pH level is as much possible. The mentioned aquarium chemicals will work the most effectively to lower the pH in aquariums, but keep in mind the health of your fish. Sudden changes in pH can increase stress in fish. Before using this product, check your aquarium pH level and contact an advanced aquarist. 










Lowering pH in salt water and freshwater tank - any differences?

One of the main differences when lowering the pH between the two types of aquarium is that the pH in a freshwater tank is different from that in a saltwater aquarium. We can't use solutions like driftwood or leaves in marine aquariums.

Moreover, chemicals and substrate will be difference. Some of them are dedicated to freshwater, others for salt water. Cannot be used in reverse.

But solutions such as: CO2 reactors, reverse osmosis or water changes will be great in both cases.


Does driftwood lower pH?

Driftwood used in tank will not only reduce pH of your aquarium, but is also a way to naturally lower this parameter. Furthermore, it will give your aquarium a more authentic appearance. Don't forget to prepare the driftwood before you put it in the aquarium.

Does AF Water Conditioner lower pH?

The AF Water Conditioner by itself does not lower or raise the pH level. But immediately after using treats a tap water, which could contain many harmful substances for fish. Reduces the level of dangerous chlorine. Binds and neutralizes heavy metals. Thanks to the protective colloid content, which replaces the natural mucus, the fish skin regenerates faster. Additionally, strengthens the immune system of fish and supports their regeneration.

Will plants lower pH in an aquarium?

Aquarium plants do not reduce the pH level, moreover, if there are too many of them in the aquarium and the lighting is too strong, then they can be the cause of a high aquarium pH.