6 Ways How To Lower pH in Aquarium Naturally & Safely

Maintaining a consistent water pH level is an essential part of keeping fish healthy. So, what do you do if your aquarium’s pH level rises or is naturally high? The good news is you don’t have to become a water chemistry nerd. Read on to find out how to lower pH levels in an aquarium safely & naturally.
How To Lower pH In Aquarium
How To Lower pH In Aquarium

Before going ahead and lowering your aquarium’s pH level, are your fish showing any signs of distress? If you answered no, I’d leave the pH level where it is.

Maintaining a consistent pH level is far more important than trying to chase the perfect pH level.

Fish are sensitive to changes in water chemistry and changing the water pH level too much will cause them stress.

What is pH?

Water pH (pH stands for potential hydrogen) is a scale that measures the number of hydrogen ions relative to the number of hydroxide ions in a solution.

In this case, the solution is the water in your aquarium.

The scale ranges from 1 to 14.

pH Scale
pH Scale

A solution with a pH level of 7 has an equal amount of hydrogen and hydroxide ions and is therefore pH neutral.

A solution with a pH level below 7 has more hydrogen ions and is acidic.

A solution with a pH level above 7 has more hydroxide ions and is alkaline, which is also referred to as being basic.

The smaller the number on the scale is, the more acidic the solution is. The higher the number, the more alkaline the solution is.

The pH scale is logarithmic, which means the difference between each stage increases by a factor of 10.

  • pH7 is neutral, so pH6 is 10x more acidic than pH7.
  • pH5 is 10x more acidic than pH6, and 100x more acidic than pH7.
  • pH8 is 10x more alkaline than pH7.
  • pH9 is 10x more alkaline than pH8, and 100x more alkaline than pH7.

You can see how a slight increase in pH level makes a massive change to the water chemistry in your fish tank.

What’s The Ideal pH For Fish Tank?

The ideal pH for a fish tank depends on the type of fish you keep.

In an ideal world, it’s best to measure your tap water pH and keep fish that are best suited to that pH level, rather than trying to manually adjust it.

Your aquarium pH level will fluctuate slightly throughout the day, it’s something that happens naturally, so when you take a pH measurement it’s important to do it at the same time of day.

Most fish can happily live in a water pH level between 6.5-8.0. 

There are a few exceptions to the rules, African cichlids for example prefer a pH of 8.0 and above, whereas South American cichlids prefer a pH of around 6.0.

I’m sure you’ve seen the shelf labels in the pet store stating what pH level a particular fish requires, this can be confusing to new fish keepers, who think they have to chase the ‘perfect pH level’ for the fish to survive.

It is much more important to keep a consistent pH level than to be chasing the ‘ideal’ number.

Fish are very sensitive to changes in pH level and shouldn’t have more than 0.3 change in 24 hours, so if you do change your pH level using any of the methods below, it needs to be done gradually.

Constantly changing the water chemistry is a surefire way to cause your fish to be stressed out, leaving them vulnerable to illness and diseases.

What Causes High pH In Aquariums?

There are a few things that can cause the pH level to rise in your aquarium.

Substrate & Tank Decor

Certain substrates, rocks, and shells are high in calcium and other minerals which will over time leach into the water and increase the pH level.

Too Many Plants

Plants are a great way of giving your tank’s nitrogen cycle a boost as they remove a lot of harmful toxins from the water, including carbon dioxide.

Carbon dioxide lowers the pH level in your aquarium water thus making the water acidic. 

However, having too many plants could deplete your aquarium of carbon dioxide and raise the water’s pH level gradually over a prolonged period.

Water Changes

If your source water has a higher pH than your aquarium water, then this will cause an increase in your aquarium’s pH level when you refill it.

Symptoms Of High pH In Fish Tank

Symptoms of having a high pH level in a fish tank include:


Your fish may show signs of chemical burns on or around their eyes, gills, and scales. These burns can be very painful, or even fatal.

High Ammonia Levels

Higher pH water makes it easier for ammonium to turn into highly toxic ammonia and you can quickly end up with ammonia poisoning on your hands.

Tank Overrun With Algae

Some algae growth is a good sign that your tank is cycled fully.

However, higher pH water can lead to rapid green algae growth which can quickly overrun your tank.

Sick Fish

If the water pH level is above what your fish can tolerate, this can cause your fish to become stressed.

Your fish may swim erratically, scratch themselves against the substrate, gasp at the surface, or try to jump out of the tank.

When a fish is stressed its immune system is suppressed leaving them vulnerable to various parasitic infections and illnesses such as dropsy, ich, popeye, and swim bladder disease.

How To Monitor pH In Aquariums

You have a few options for monitoring your water pH level.

Water Test Strips

API 5 in 1 Test Strips

Water test strips are a quick, easy, cheap, and convenient method of testing your water’s pH level.

Simply dip the test strip in and out of the water, wait for however long the instructions say, then compare the color of the test strip to the color chart that came with the kit.

The kits increase and decrease in 0.5 increments so you have an idea of roughly where your water pH is at.

Aquarium water test strips can also simultaneously test pH, kH, nitrate, nitrite, ammonia, iron, and other useful measurements.

Water Test Kits

API Freshwater Master Test Kit

A water test kit will require you to add some tank water and test solution to a test tube and wait for the color to change.

As with the test strips, compare the color of the water to the color chart that came with the kit.

They’re inexpensive and accurate, but there’s a bit more work involved than using a water test strip kit.

Digital Gauge

PH Meter for Water Hydroponics

My preferred method of monitoring my water pH level is with the Ruolan digital gauge.

While the test kits and strips work well and are convenient, the digital gauge is much more accurate than relying on comparing a vague color chart.

A digital gauge gives you measurements to within 0.01 instead of 0.5, so you’ll know exactly where your water pH level is at.

How Often Should I Test Aquarium pH?

I test my tank water pH weekly along with the ammonia, nitrite, and nitrate levels.

Testing regularly and logging the test results down on a chart will help you keep on top of keeping your aquarium water safe and stable for your fish.

You’ll soon be able to spot when something isn’t right and take the necessary action to fix it.

Test your water at the same time on your chosen day to ensure the most accurate and consistent results, as pH naturally fluctuates throughout the day.

How To Lower Aquarium pH Naturally?

If you find that you need to lower your aquarium pH, there are a few great options.

1. Driftwood

Driftwood for the aquarium

My No.1 choice when it comes to lowering aquarium pH is driftwood.

Not only does it look great, but it also provides fish with somewhere to hang out and unwind.

Driftwood slowly releases tannins into the tank water giving it a yellowy brown coloration.

If you don’t like the coloration you can add some activated carbon to your filtration system.

Make sure you buy aquarium safe driftwood. Wood that is designed for a reptile enclosure could have other chemicals in it that are harmful to fish.

I highly recommend sanding down any sharp points on the driftwood to avoid your fish injuring themselves.

2. Catappa Leaves (Indian Almond)

Catappa Leaves

Indian almond leaves are a great addition to your fish tank. Like driftwood, they lower the water pH level by slowly releasing tannins and they also have antibacterial properties.

These leaves help to maintain your fish’s slime coat and help towards preventing fungal and bacterial infections.

The tannins released will turn your tank water a browny yellow color. The coloring is harmless to your fish, but if you don’t want it, add some activated carbon to your filtration system.

The leaves will float around your tank which looks natural, but it’s not to everyone’s liking. You could tie a few together and place them inside your filter if that’s the case.

You’ll have to replace the catappa leaves periodically as they decay in the water. How long this takes depends on the water chemistry in your tank.

3. Peat Moss

Fluval Aquatic Peat

Peat moss is another naturally found substance that’s great for lowering your water pH level.

The key with peat moss is adding a little bit at a time over several days and keep monitoring the water pH level. If you add too much too soon you could see a huge drop in water pH.

Like driftwood and catappa leaves, it releases tannins into the water and could turn your tank water to the color of tea.

To minimize this, you could soak the peat in clean water for 4 days before adding it to your fish tank.

When you do add it, put it inside a filter bag and hang the bag where there is good water flow so the tannins get all around the aquarium.

If you don’t put it inside a bag it will float around the aquarium and look unsightly.

My preferred method is to place the bag of peat moss inside the filter.

4. Reverse Osmosis

iSpring RCC7, NSF Certified, High Capacity Under Sink 5-Stage Reverse Osmosis Drinking Filtration System

The iSpring RCC7 5-stage reverse osmosis filtration system is a great RO system.

Using this method won’t discolor your tank water like catappa leaves, driftwood, or peat moss will.

A reverse osmosis filter works by filtering out mineral deposits and chemicals like pesticides and heavy metals in water.

An RO system is not the cheapest way of lowering your aquarium’s pH, but you do get the added benefit of having nice clean drinking water too!

Something to be aware of with some cheaper RO units is that they don’t remove chloramine from the water, so you would need to do that separately if your tap water contains chloramine.

5. CO2 Injection

MagTool 4L Aquarium CO2 Generator System

I don’t recommend this method to beginners.

A CO2 generator is used in planted aquariums, plants feed and flourish off the additional CO2.

When CO2 dissolves in water it releases a small amount of carbonic acid, which increases the acidity in the water, causing the pH level to drop.

It’s important to use a timer with CO2 injection and only have it running when the aquarium lights are switched on. 

If it is left running at night when the plants do not photosynthesize, you can end up with excessive levels of CO2 in your tank, causing the pH levels to plummet.

6. Water Changes

Python No Spill Clean and Fill Aquarium Maintenance System

Regular tank maintenance and water changes are essential parts of keeping your water parameters in check.

Changing 25% of your tank’s water will help with removing ammonia, nitrite, nitrate, compounds, and minerals that are contributing to the pH imbalance.

I have a detailed guide on how to clean a fish tank that will take you through this process step by step.

How To Lower pH In Aquarium FAQ

Some questions I hear a lot on how to lower pH in an aquarium are:

Why Is My Aquarium pH So High?

There could be any number of reasons why your aquarium pH is high.

The first thing to check is the tap water that you use to fill your tank. Is that a high pH? If so use one of the methods above to lower your water pH level.

If the pH of the tap water is ok, something within your tank is causing the pH level to rise…time to investigate…

Do you have an alkaline substrate or any decor items that are leaching minerals into the water?

Do you have too many plants in your tank?

How Do I Fix High pH In My Aquarium?

The best ways to fix high pH in a fish tank are the solutions I suggested above, driftwood, capatta leaves, peat moss, a reverse osmosis device, or a CO2 injector.

Can I Lower pH In Aquarium With Vinegar?

Yes, you can lower your aquarium pH with vinegar, but you need to measure the vinegar carefully to avoid a huge pH swing.

I recommend using a syringe to get an accurate measurement.

Before you add any vinegar, take a reading of your aquarium’s pH level so you know how much you need to lower it.

Add only 1ml of vinegar per 1 gallon of water. The ratio has been proven to lower your aquarium pH level by 0.3, the maximum pH level change you should expose your fish to in 24 hours.

Add the vinegar to an area of high water flow so it gets mixed properly around the tank.

After 24 hours have passed, test your water pH again to see if you need to add more vinegar to your tank water.

What Happens If pH Is Too High In Fish Tank?

Having a pH level that’s too high can be disastrous for your fish’s health due to them receiving chemical burns around their eyes, gills, and scales.

They can become stressed out which leaves them vulnerable to various bacterial and parasitic infections and illnesses.

Final Thoughts On How To Lower pH In An Aquarium….

I’m a big believer in the adage ‘if it ain’t broke, don’t fix it.’

As I’d said in the intro, if your fish are healthy, don’t risk stressing them by lowering your water’s pH level if you don’t need to.

If you have to lower it, my preferred method is by adding aquarium-safe driftwood to the tank or adding Indian almond leaves.

For more guides on keeping your tank in tip-top shape, check out the aquarium health section.