9 Ways To Lower Aquarium pH + Symptoms & Causes

As the care keeper of your aquarium and fish, it’s important to know how to keep a consistent pH level and how to lower the aquarium’s pH if necessary (As well as raise it).

A pH level that is too high can 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/alkaline 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 your fish can use it. In the case of heavy metals, their toxicity is based on how soluble they are. Because they are more soluble at lower pHs, this is when they tend to be more toxic to your fish.

How To Deal With High pH In Your Fish Tank

What is the pH Scale?

The pH scale determines how acidic or alkaline water is. The scale ranges from 0 to 14, where 7 is a neutral number. Acidity is indicated by pH values below 7, whereas alkalinity 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.

Signs Your Fish Tank Has High pH Levels

There are some tell-tale 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 Gills Are Damaged By High pH Levels

Fish gills can be compared to your lungs. They allow the fish to breathe, but unlike us, they are designed to live in water. If the pH levels jump, the gills will become damaged, making it hard for the fish to breathe.

Skin On The Fish Will Become Damaged

The mucus located within the skin will become damaged. This mucus protects the skin from moisture, which is why the skin on the fish will become damaged and start rotting away.

Fins On The Fish Will Deteriorate

High pH levels will cause damage to the fins of the fish, which is easily seen on the bigger fins around the tail and the top of the back.

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, 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 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 really depends on the areas your fish originally came from, as well as the tanks they have been kept in all their lives. GENERALLY though, the ideal pH for aquariums is between 6.0-8.0.

What’s arguably more important than the pH itself is making sure that the pH doesn’t swing. A stable pH that is a little bit off, is still going to be better than a pH that is constantly swinging.

goldfish swimming together

How to Safely Lower Your Aquariums pH Level

If your pH is too high, then fortunately, there are a number of not only effective, but also cheap ways to lower it, so your fish can stay happy and healthy! So try any of the following.

Peat MossNatural method using peat moss in the filter.Safe, naturalMay discolor water
DriftwoodIntroduce driftwood into the tank.Aesthetic, naturalMay harbor bacteria if not sourced properly
Catappa LeavesUse Indian almond leaves.Antibacterial propertiesDarkens water
Chemical SolutionsUse pH Down or other chemicals.Quick actionMay require frequent adjustments
Reverse OsmosisUse a water filtration system.Effective, preciseComplex maintenance
Water ChangeReplace some of the tank water.Quick, simpleTemporary solution
CO2 ReactorsIntroduce CO2 for live plants.Helps plants growRequires monitoring
VinegarUse vinegar to adjust pH.Quick, easyControversial, temporary

Peat Moss

Peat moss is an amazing natural method that safely lowers the pH in your freshwater aquarium and filters impurities from the water.

However, aquarium water may occasionally become discolored and become blackwater when using peat moss, but this problem will soon go away. And this blackwater, actually mimics a fish’s natural habitat a lot better!

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.

Fluval Aquatic Peat Granules, Chemical Filter Media for Freshwater Aquariums, Water Softener, 17.6 oz., A1465
  • Filter Compatibility: Compatible with Fluval filter models: 106, 206, 306, 406, FX5, FX6, 105, 205, 305, 405, 104, 204, 304, and 404.


Driftwood is another 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 help lower the pH in your tank. Similar to peat moss, introducing driftwood will naturally tint the water, giving it a blackwater effect.

Remember, you should always buy your driftwood from a reputable source, and avoid using some you find yourself as it could be covered in bacteria and parasites. As well as this boil it briefly before adding it to your tank.

emours Aquarium Driftwood Fish Tank Decoration Varies Shape and Size (Medium)
  • Made of high grade driftwood, solid and durable, long lasting in underwater or arid environments

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.

Premium Indian Almond Leave. Aquarium Decorations Size 6-9″ Pack 50g(20-25 Leaves). Catappa Leaves Rich in Tannin. Superb to be Health Better, Vitality, Succesful Breeding! of Shrimp & Betta Fish Tank
  • 🍀 SUPERB FOR HEALTH OF YOUR BETTA FISH AND SHRIMP – Betta leaf rich in Tannin. it helping the betta fish and shrimp health to be noticeably better. And Enhances the natural color of to them.

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.

However, if you need the pH to go below the designated range of standard chemical buffers, you can also use pH Down for aquariums.

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 re-add any mineral that your fish would normally absorb from the water.

LiquaGen- 5 Stage Reverse Osmosis & Deionization (RODI) | Aquarium Reef Water Filter System – 75 GPD | Water Purifier for Fish Tank with Filter’s Included
  • This 5 Stage Aquarium Filter Machine is an excellent Pre-Assembled Reverse Osmosis System to eliminate small impurities like chlorine found in city water. This machine requires minimal space! Ideal for Aquarium Water Treatments like Fish Tank’s, Reef Tanks, Saltwater and Freshwater Aquariums; also for laboratory testing, and other applications where ultra-pure water is necessary. Optimal water filtration for fish, coral, turtle aquarium’s & other aquatic life, live rock & plants.

Change the Tank Water

In a lot of cases one of the quickest ways to change the pH in the aquarium is simply by changing the water. As long as the water you’re adding has a lower pH than the water in the tank, it’s going to dilute the original pH.

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.

MagTool 4L Aquarium CO2 Generator System Carbon Dioxide Reactor Kit with Regulator and Needle Valve (2.5L with Solenoid)
  • 2.5 Liter Capacity. Holds 300g-400g of citric acid and sodium bicarbonate, aka baker soda powders.

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. If the filter in your tank isn’t effectively, the ammonia in your tank will begin to build up. And believe it or not, ammonia has alkaline properties, so it may end up causing the pH to rise.

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.

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.

What Causes High pH In Your Aquarium

There are a few common causes of high pH levels in your fish tank. You must remember that life within your aquarium is delicate, and they need constant care and supervision to maintain good health.

Calcium-Rich Decorations Can Cause High pH

One of the most common causes of high pH levels is the ornaments you buy off the shelf. They are loaded with calcium, which is a mineral that raises the amount of pH in the water.

Low CO2 Causes Low pH

Low pH is not as dangerous as high levels but can still cause havoc in your tank. The more aeration you have going into the tank, the less CO2 you will have in the water. When this happens, the pH will drop.

Using Tap Water Is A Common Cause Of pH Fluctuations

Tap water is something you should avoid using at all times when it comes to the water in your fish tank because it can cause a drastic increase in the pH levels. Always use distilled water when filling or adding water to your aquarium.

Old Filters Can Cause High pH Levels

Even if you think the filters still look good, change them regularly. The back of the box should tell you the suggested length of use of the filter you have, so make sure that you follow the manufacturer’s suggestions.


Here are some frequently asked questions that people have about high pH levels in their tank and what they can do to lower them!

Can You Use Vinegar To Lower The pH In A Fish Tank?

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. 

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. 

How Often Should I Test the Water in My Aquarium?

How often you are testing your water depends on the health and age of your tank. Newer tanks should be tested every few days to ensure there are no water quality issues.

The same would apply if you have algae growth or there are concerns with fish health. Established tanks should be tested every two weeks to one month to ensure there is no need to change the established routines. 

What Is the Ideal PH Level for Planted Aquariums?

It would depend on the fish and plants you are maintaining. Most aquariums are kept in the 6.0- 8 pH range. The water in your aquarium should be tested at least once a week to maintain quality and fish health.

What Are The Best Plants to Lower PH Levels in My Aquarium?

While plants themselves aren’t going to lower the pH in your aquarium, if you want something natural to do the job, then you should add driftwood, Indian Almond leaves, or peat moss to your tank.

What Are Tannins and How Do They Affect Your Aquarium?

Tannins, also known as tannic acid, are released by the decay of driftwood and plant matter in your tank. They are not only great for lowering the pH in your tank, but they also have antibacterial properties which can keep your tank cleaner.

Is a pH of 8 Too High For Your Aquarium?

Between 6.8 and 8 pH is where you want the water in your tank to be tested. 8 is the highest you want to ever let your tank get to unless you are keeping all fish that enjoy it a little higher. For most fish, though, keep it at 8 or lower.

betta care facebook group


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.

About the author

Hey! I'm Antonio!

Betta fish keeper for over 6 years now! Since owning a betta I've also housed all kinds of tropical fish, and have seen all manner of problems and how to look after them!

If you need any advice you can always message me or better yet join the Facebook group where a community can answer your questions!