10 Ways To Lower Aquarium pH (& Why It Happens)

When you’re an owner of an aquarium filled with fish, it is important to know how to keep a consistent pH level and how to lower the aquarium’s pH if necessary. A pH level that is too high can cause put stress on your fish and even cause them to die. In this article, we’ll explore what pH is and how to safely lower pH levels in your aquarium.

What is pH?

pH is a measure of how acidic/basic water is at any given moment. The pH of water controls the biological availability (the amount that can be consumed by aquatic life) and solubility (the amount that can be dissolved in the water) of chemical components like nutrients (phosphorus, nitrogen, and carbon) and heavy metals (lead, copper, cadmium, etc.).

For instance, pH affects not only how much and in what form phosphorus is most prevalent in the water but also whether marine life can utilize it. In the case of heavy metals, their toxicity is based on how soluble they are. Because they are more soluble at lower pHs, metals tend to be more toxic.

Signs Your Fish Tank Has High pH Levels

There are some telltale signs to look for in an aquarium that needs its pH levels lowered. Some will be much more obvious than others, but if you know what to look for, you can spot even the smallest change.

Fish Behaving Oddly

If you notice that your fish may be behaving a little bit differently than normal, this could be an indicator that the aquarium pH levels are off. Keep a close eye on your pets and watch their behavior from time to time to ensure their environment is healthy.

Fish Exhibiting Signs of Alkalosis

Alkalosis is an illness that can is caused by high pH levels in fish tanks. If your fish begin swimming around quickly and wildly or they begin to show excessive excitement for long periods of time, this could be a sign that you need to lower the aquarium pH.

Fish May Develop Ich

Another illness that is caused by high pH levels in a fish tank is known as Ich or Ick. Signs to watch out for include white spots all over their body, bloody-looking streaks on their fins, and using rocks or the side of the tank to “itch” themselves.

Tank May Grow Algae

In an aquarium that has high alkalinity, the tank itself may begin to show signs that you need to take action to lower the pH. Green algae may grow on the structures and walls of the tank at an increased pace and can cause the water to become toxic to fish.

Fish May Breathe on the Surface

If you notice that your fish seem to be heading towards the surface to take a breath, it may be time to check those pH levels. This can be a sign that the pH levels are too high for the fish to breathe normally in their environment.

What is the Ph Scale?

The pH scale determines how acidic or basic water is. The scale ranges from 0 to 14, where 7 is a neutral number. Acidity is indicated by pH values below 7, whereas baseness is indicated by pH values above 7. The pH of water is a crucial indicator of the purity of the water.

All liquids fall somewhere on the pH scale. For example, things like bleach, ammonia, or drain cleaner all fall above a seven on the pH scale, so, therefore, they are more alkaline. Battery acid, black coffee, and lemon juice, however, all fall below a seven making them more acidic liquids.

What Is the Ideal PH Level for an Aquarium?

Many people may wonder what pH the water should be kept at when owning fish. The solution is not so straightforward because not all fish breeds respond to the same pH.

This is due to the wide variety of habitats that fish inhabit; some come from the ocean, others from rivers, and still others from brackish environments, which fall somewhere between the two in terms of salinity.

However, in general, saltwater fish prefer slightly alkaline conditions, whereas freshwater fish prefer water that has a pH between 5.5 and 7.5. Keeping your pH at the right levels depending on the breed of fish you have is important to their overall health and longevity.

How to Safely Lower Your Aquariums pH Level

As mentioned previously, it is very important that you maintain the pH levels in your fish tank at a proper level for the specific type of fish you have. A pH too high could result in any number of ailments for your pets or even death. Below are some examples of methods you can use to safely and effectively lower aquarium pH levels.

Peat Moss

Peat moss is an amazing natural method that safely lowers the pH in your freshwater aquarium and filters impurities from the water. By attacking the bicarbonates in aquarium water, the peat moss’s tannic and gallic acids lower the pH and lessen the hardness of the water.

The aquarium water may occasionally become discolored when using peat moss, but this problem will soon go away. Some hobbyists prefer this, but if you are hosting guests and don’t want your aquarium water to become tinted, you can pre-treat the water in a different container for a few days prior to actually adding it to your aquarium.

Peat moss must remain in your aquarium; dipping it in and out will not work to lower the pH effectively. Purchasing pellets or chunks of peat moss and adding them to your aquarium filter is the simplest way to use it.

Since there are still no precise dosage instructions available, we advise you to work with a small piece and add more if necessary after checking the pH with pH strips or a pH meter. To regulate the water chemistry in aquariums before trying to add plants and fish, peat moss is frequently used.


Driftwood is a natural component of a fish’s natural habitat, so in addition to having a fantastic aesthetic effect, it will also end up making your fish feel more at home.

Driftwood emits tannin, which can cause your aquarium’s pH to decrease. Similar to peat moss, introducing driftwood will naturally tint the water, which won’t strain your fish or hurt any plants.

Check that the driftwood is suitable for aquariums before adding it because not all driftwood is suitable for freshwater aquariums. Just in case, we advise adding extra security measures!

When you have your portion of driftwood, it is advised that you sterilize it by boiling it in salt water. This helps to avoid the wood tarnishing the aquarium water and makes sure there is no dirt, fungi, or other debris on it.

Chemical Solutions

The advantages of chemical solutions include their immediate effectiveness and speedy pH correction.

Chemical products function as a buffer to stabilize and maintain the pH level of the water in your aquarium within a predetermined range. Depending on the dosage you use, you can modify this range.

These goods introduce molecules that absorb hydrogen atoms, offsetting the pH. For this purpose, phosphate, bicarbonate, and carbonate are frequently used in products. They will be a fantastic addition to your setup and are okay for marine and plant species.

Catappa Leaves

Indian almond leaves, also known as catappa leaves, are a traditional remedy for bacterial and fungal infections.

They release tannins into the water, making them a fantastic asset to your aquarium. Additionally, if your fish have lost their slime coat, their antibacterial properties can help keep them healthy.

Catappa leaves can be placed on top of the water to start creating some shade, which is good for some species of fish but not the best for others. Additionally, you can pulverize dried leaves and add them to the water. Be aware that catappa leaves can give your water a dark tint.

Reverse Osmosis Units

Water filtration systems include reverse osmosis systems. These filters force water through a thin membrane that picks up tiny particles that another purification medium might miss.

Reverse osmosis filters have the advantage of being able to remove solids that have dissolved in the water, such as chlorine, toxins, or minerals. It aids in water purification and helps get rid of the substances causing the pH imbalance.

If you want more control over your setup, using a reverse osmosis filter is a good choice. However, you should be aware that this increases the complexity of tank maintenance because you must reintroduce the beneficial properties the filtration system removed (https://atlas-scientific.com).

When Is It Necessary to Lower the PH in Aquariums?

It is necessary to lower the pH in aquariums when the tank is growing algae at an increased rate or if you notice your fish exhibiting odd behavior or any of the illnesses that were mentioned previously.

Most times, depending on the breed of fish, your fish will adapt to the tank’s pH levels as long as it is stable and within the range that is common for their environment. In fact, it can be harmful to your fish to change the pH frequently.

Only change the pH levels if you have checked the numbers and it seems too high and if your fish have begun behaving in a peculiar way.

Other Ways of Lowering pH in An Aquarium

There are a few other tried and true methods to lowering the pH levels in your fish tank.

Change the Tank Water

An important component of aquarium maintenance is routine water changes. Depending on the size of your tank, you should perform water adjustments every two to four weeks, changing 15 to 20 percent of the water.

A pH imbalance, however, might necessitate more regular water changes. Additionally, you can charge more than 20% of the overall water in the aquarium.

When changing the water, you also remove other substances that contribute to the pH imbalance. Additionally, you are adding neutral pH water from an outside source, which should greatly reduce the concentration of hydrogen ions responsible for the pH imbalance.

The pH will start increasing again if there is an issue with your setup, though. Water changes aren’t a long-term fix, but they are an essential first step in reducing the impact of high pH levels and keeping your fish alive until the underlying problem can be resolved.

Carbon Dioxide Reactors

A CO2 reactor might be a wise purchase if your freshwater aquarium contains a lot of live plants.

For your plants to thrive, carbon dioxide reactors ensure a steady flow of CO2 into the aquarium water. As long as a reactor is running, CO2, which has a mild acidic nature, can help lower the pH in your aquarium.

Find yourself a nice CO2 sensor and an O2 sensor so you can monitor the amount of carbon dioxide and oxygen (O2) in your aquarium.

Using Rocks or Gravel That Contain Limestone

The majority of rocks won’t change the pH of a freshwater aquarium. However, limestone-containing rocks will undoubtedly affect the pH of your water. Calcium carbonate, the main component of limestone, is naturally basic and raises pH levels.

Simply drop some vinegar onto your rocks to see if they contain limestone. Limestone-containing rocks will cause the vinegar to bubble and fizzle.

Check Filters and Change Them Often

To lower the pH levels in the aquarium and keep them at a stable level, it is important to check your filters often. If your filter seems old and dirty, it may be time to swap it out for a new one.

Filters are a crucial part of any fish tank that requires routine maintenance to keep the environment stable and healthy for marine life.

Vinegar to Lower pH

Some aquarium owners claim that using vinegar can lower the pH levels in a fish tank. Although this is a temporary solution, they claim it can be effective.

Other fish enthusiasts urge owners not to use the vinegar method because if it is done incorrectly, it could do more harm than good.

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Can you use vinegar to lower the pH in an aquarium?

As mentioned above, you can, in fact, lower pH levels in an aquarium using vinegar. It is important that you know the ratios you are working with so as to not add too much vinegar and cause more harm. 

It is suggested that for every gallon of water, you should only be using about 1ml of water in your aquarium. This will only lower the pH level by a few small increments, but it can buy you some time to find a more permanent solution. 


As you can see, there are many effective methods to utilize to lower the pH in your aquarium. A stable pH makes for a healthier environment for your fish to grow and thrive.

pH levels can be lowered in numerous natural ways or with the help of filtration systems; you only need to find which one will work with your aquarium the best.