How to Lower pH in Aquarium – 9 Tested Methods + More

Keeping consistent water parameters is essential for every aquarist. As such, you need to know how to lower the pH in the aquarium once the levels become too high.

Sudden water changes in the tank are never good for the fish. You need to know how to maintain the water quality, and this includes the aquarium’s pH.

Luckily, you don’t need expensive products or equipment. You might not even have to change the entirety of the tank water! Here’s how to lower pH in the aquarium in 9 tested ways. 

Let’s get started!

How Do I Bring My pH Down?

While low alkalinity levels are a problem, having too high pH values can also cause many issues for the fish. 

In general, salt water tanks should have a pH of 8.0 – 8.4, while freshwater aquariums  should have pH levels between 6.8 and 7.8. Anything higher or lower than that isn’t good and it’s disrupting the water quality. 

There are many ways you can raise your pH levels. However, as you’re here, I’d suppose your problem lies on the other side. You want to know how to lower pH in the aquarium, and you probably wonder whether there are some natural methods to do just that. 

Well, you’re in the right spot! I’ve tested several methods of lowering alkalinity levels, and I’ve found 9 helpful tips. 

Here’s what might help you:

1. Driftwood

Adding driftwood is probably the easiest and most effective way to lower the pH of the water quickly. In fact, you might be doing this without even realizing it!

Driftwood is one of the most gorgeous decorative items people put in their aquariums. In fact, chances are you have one in your tank already! It is naturally found in most fish’s environment, making it seem that this is a safe and pretty addition to your tank.

Despite this, not many people realize that driftwood can lower the aquarium pH, which often causes more problems than you might think. Still, as I presume you’re someone struggling with too high pH levels, this is good news for you.

Driftwood will release tannins or tannic acids when in contact with water. This will increase the water’s acidity, lowering the pH levels.  

In fact, if you’ve noticed your tank water becoming tinted after introducing driftwood, now you know why this happens. It’s all due to tannins!

If you don’t have alkaline water, boiling driftwood before placing it into the water is a necessary step. However, if you want to use it as a tool to keep desired pH levels, skip the boiling bit. 

Just remember to make sure you’re using driftwood suitable for aquariums! 

2. Peat Moss

Peat moss is loved by many aquarists due to the numerous benefits it has. Not only will it help filter the water, but it will also make sure your pH levels aren’t too high.

Just like driftwood, peat moss will emit tannic acids. Next to that, it is also rich in gallic acid that attacks bicarbonates in the water, making this the preferred way to keep low pH levels by many aquarium hobbyists. 

Just like driftwood, peat moss might tint the water inside your aquarium. Don’t worry – unless your pH levels weren’t too low before, this won’t harm the fish. 

An important tip is that peat moss won’t suddenly change the water chemistry. It takes some time for your aquarium pH levels to drop. Make sure you leave it in instead of simply dipping it into the water. 

A good idea is to add peat moss to your filter. This will ensure the changes are slow yet long-lasting. 

It’s important to note that there is no precise dosage when it comes to peat moss. As such, I would advise you to start with small pieces, wait a few days, then add more if necessary.

3. Catappa Leaves

Catappa leaves, also known as Indian almond leaves or terminalia catappa  leaves, are commonly used to treat fungal and bacterial infections in fish. Next to aquarium salt, both store-bought and the one you might make at home, it is one of the most common remedies.

At the same time, Catappa leaves are yet another great source of tannins. They will lower the pH levels while also keeping your fish healthy!

In fact, this makes them an amazing choice if your fish have already sustained some damage from inappropriate alkalinity levels. They’ll fix the aquarium pH and reduce health issues due to their antibacterial properties.

All you need to do is put Catappa leaves on top of the tank and let them float, creating a shade for your fish.

Still, it’s important to note that not all breeds of fish will like this. Some types of fish prefer having as much light as possible and having leaves floating above them will stress them out. 

The solution to this is to pulverize dried leaves and add them to your tank water. Just keep in mind that this, too, will cause water discoloration.

4. Vinegar

This might be a great solution for those looking for natural ways to lower pH in aquariums. However, I’ve found it to be tricky and it can do more harm than good.

Vinegar is acidic. That’s why it adds that taste to our salads and food. If you add it to the tank water, you will notice that its pH levels will immediately drop.

However, I need to add an important disclaimer: If you do this method incorrectly, you are risking the lives of your fish.

The recommended amount of vinegar is 1ml per 1 gallon of water. I have added even less vinegar (about 0.5ml) and it still worked fine. It’s better to use small amounts than to go overboard. 

This will immediately lower the tank’s pH value by approximately 0.3.

As you can see, this is a quick solution and it does work. Vinegar will certainly lower pH inside your tank. 

Despite this, there are many risks with this method. This includes:

• Too sudden changes will stress your fish out. This might even cause severe health problems.
• Adding too much vinegar can make your water too acidic. 
• You don’t have much control over pH levels as in most other methods.

With so many different ways to create more acidic water, I don’t see why you should risk it by adding vinegar. Still, this is an effective method and it will do precisely what it’s supposed to. 

5. Replace the Filters

Filters ensure steady oxygen flow inside your tank. With its help, you can be certain your water parameters will stay stable. 

However, even filters aren’t everlasting. You need to check them out from time to time to make sure they aren’t dirty or clogged. 

Even with best maintenance, if you’ve noticed your filter malfunctions often, it’s time to get a new one. 

6. Reverse Osmosis

Another way to keep your aquarium stable is to use filters with reverse osmosis units. 

Reverse osmosis units have semipermeable membranes  that can collect any impurities other types of aquarium filters might have missed. This includes various minerals, but also toxins and chemicals such as chlorine commonly found in tap water.

By removing all impurities, reverse osmosis filters will make sure you have balanced pH levels and water hardness.

The biggest issue with this method is that reverse osmosis units will remove many beneficial bacteria and minerals from the water, as well. This means you’ll have to reintroduce anaerobic bacteria and healthy levels of minerals.

In other words, while this might be a great way for lowering pH values, it requires more maintenance. Not everyone will be okay with that.

7. Carbon Dioxide Reactors

Does your aquarium contain lots of aquatic plants? If it does, you might want to consider buying a carbon dioxide reactor for your tank, especially if you struggle with high pH levels.

High oxygen levels are known to raise pH levels in the tank. While you want to have enough oxygen for all your tank inhabitants, you can still have too much. This is where carbon dioxide reactors come into play.

Carbon dioxide helps plants by, as its name suggests, creating carbon dioxide and ensuring its steady flow. With it, your plants will thrive.

More importantly, carbon dioxide is slightly acidic in nature. This is due to pure science

In contact with water, carbon dioxide turns into carbonic acid which breaks into hydroxide ions and bicarbonate ions. High hydrogen ion concentration lowers pH. In other words, hydrogen atoms make the tank water more acidic.

You can buy carbon dioxide reactors in most larger pet stores. They come in several sizes, and you should choose one according to the size of your tank.

Just make sure to monitor carbon dioxide levels all the time. You don’t want your fish to suffocate due to lack of oxygen!

8. Chemical Solutions 

Another possible way to make your water more acidic is to use one of many readily available chemical solutions – also known as aquarium buffers. 

Aquarium buffers will help regulate the pH levels of your aquarium water and keep them within a specific parameter. You can choose between lower or higher values of pH by adjusting the dosage.

Most buffers are perfectly fine for both marine and freshwater fish. They’re easy to use and mostly inexpensive, which is why many aquarium hobbyists prefer using them over most other methods, including using various natural or organic materials. 

9. Change the Water

Finally, the last step might be to change the water entirely. 

Regular water maintenance is essential for having proper alkaline conditions. It’s suggested you change 10-20% of the water each week, or at least 30% twice a month. This will also help you keep the tank water clean without removing the fish.

By doing this, you’ll remove all impurities, while also adding fresh water with optimal levels of pH. 

However, when your water becomes too contaminated or your pH levels are too much out of balance, a complete water change might be necessary.

Just keep in mind that this should be your last choice, although it probably is the only permanent solution. Making such a huge water change will stress your fish out. If you do it too often, you’ll do more harm than good.

Does Baking Soda Lower pH?

There is a common misconception that you can lower pH in aquariums by adding baking soda. 

Baking soda, or sodium bicarbonate, is an alkaline chemical often used in our kitchens. It’s used for many different purposes. You can even clean limescale with it!

However, baking soda will raise ph levels inside your tank, not lower them. It will do the exact opposite of what you want. 

If you want to have more acidic water, never add baking soda to your aquarium!

What Does Baking Soda Do to Fish?

In general, baking soda won’t harm the fish in your tank. There are even several pieces of research that have shown that sodium bicarbonate can be used as a natural anesthetic for fish!

However, if you put too much baking soda inside your aquarium water, the water will become too alkaline. This can severely harm your fish.

Unless you’re deliberately trying to raise pH levels in your tank, don’t put baking soda anywhere near your fish!

What Causes High pH in Fish Tanks?

You cannot fully understand how to lower pH in an aquarium without learning what causes high pH in the first place.

Most of the time, high pH is caused by poor tank management and irregular cleaning. 

However, there are a few other things that might raise your pH levels, such as:

• Adding limestones and other decorative items made out of calcium carbonate.
• Using tap water, rainwater, water from streams and boreholes, and so on.
• Certain fish foods and supplements can raise pH levels, especially if you commonly have leftovers.
• Depletion of live plants.
• Fish waste.

What Happens if Fish Tank pH Is Too High?

If the water inside your tank has pH values over 7.5, it is considered slightly alkaline. However, just how much is too high greatly depends on the fish species you have in your tank. 

Marine breeds of fish can tolerate higher pH levels than freshwater fish. In fact, they prefer somewhat higher pH, so you can keep your salt water at around level 8.

Still, anything higher than 8.5 is usually considered too alkaline. Such high pH levels can cause severe health issues to your fish, including fish itch, burns, and inability to dispose of metabolic wastes.

pH of 9.6 is considered very alkaline and this is the point at which most fish cannot survive.

Not just that, but alkaline water might make other substances toxic. Also, too high pH levels will increase ammonia levels, killing all the fish in your tank.

Symptoms of High pH in Fish Tank 

There are several ways you can tell the water in your tank has gotten too high. 

Of course, the safest way to find out is to buy a testing kit. They aren’t expensive and they can let you know if other water parameters are out of control, as well.

Not all of us have testing kits at hand. Also, let’s face it, no one checks water parameters as often as they should!

Fortunately, there are some telltale signs that your pH levels are too high. Here are some of the most common ones:

• Your fish are behaving in an unusual way. Fish will feel pH changes and this will stress them out.
• Damaged gills in fish. Gills are the first fish’s body part that will experience damage due to high pH levels.
• Deteriorated skin of the fish. Alkaline waters will harm the mucus on the fish body, causing skin issues.
• Increased algae growth. Algae will overgrow in water conditions that are improper for most other living beings, including fish. Whether your pH levels are too high or too low, expect to see green buildup on your tank.
• Dead fish. Finally, high alkaline levels might kill a large number of fish inside the tank. Fish might die either from water toxicity or, more often, from diseases such as fish itch.

Final Word

Now you know how to lower pH in an aquarium. While many aquarists think that you should only worry about too low pH levels, high levels can be just as dangerous.

It isn’t that often that you’ll find that your pH levels have gone too high. Most of the time, you’ll likely deal with the opposite situation and too low pH. This, however, doesn’t mean you should be unprepared. High pH levels can kill your fish rather quickly.

Of course, you shouldn’t just look for a way to lower your pH. You need to eliminate the cause. High pH levels are an indication that something is severely wrong with your water quality.

Still, I hope these methods can help you find out what went wrong and ensure your fish have healthy, long lives.