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How To Lower PH In Fish Tank: Complete Guide

Snippet: You can lower your aquarium’s PH by using chemicals, natural products such as peat moss, or filters. You can lower the PH too much if you aren’t careful.

If your aquarium’s PH goes either too high or too low that can bother, harm, or kill your fish. Plants also need the right PH balance to be healthy. If you have an aquarium, you should know how to lower the aquarium PH.

If your PH goes too low, the water becomes acidic. If the PH goes too high, the water becomes alkaline, which is just as dangerous. There are many natural and artificial ways to correct this problem before it gets any worse.

Some people use chemicals or filters to lower the water’s PH. Others use natural methods – for example, you can add certain types of wood to the tank to lower the PH. There are a few different ways to test the water to make sure that the PH level is neither too high nor too low.

What is PH?

PH is a measure of how alkaline or acidic your water is. PH stands for “power of hydrogen” and refers to how many hydrogen ions are in the water.

Acids have very few hydrogen ions, alkaline substances have very many of them. PH is a scale from 0 to 14. Very powerful acids that dissolve metal and injure people who touch them have a PH close to zero. Very alkaline substances, which are also dangerous chemicals, have a PH close to 14.

When two substances that differ in PH come into contact with each other, a chemical reaction occurs. The simplest way to demonstrate this is with baking soda and vinegar. Vinegar is a weak acid (that you can even use to lower the PH for an aquarium), and baking soda is alkaline. When the two mix together, lots of bubbles and gas appear.

These chemical reactions can make acids and alkaline substances dangerous to people, plants, and animals. High PH is just as dangerous as low PH. Bleach and other cleaning solutions, which have PH levels of 11. 12. or 13. are just as hazardous as acids are.

While a weakly acidic or weakly alkaline substance won’t hurt anyone or anything, it can do harm in the long run. Fish cannot live in an alkaline environment forever. After a while, the higher than normal PH will make them sick or kill them.

A difference of only one or two points on the PH scale means that the water is drastically more acidic/alkaline, not only a little more. If the PH increases from 7 to 8, that means there are ten times as many hydrogen ions in the water. A PH of 9 means a hundred times as many hydrogen ions as a PH of 7.

For this reason, even a shift of a single point in either direction can be catastrophic. The safe range is much less than a full point in either direction.

Different Fish Need Different PH Levels

In different parts of the world, the PH of the water is different. In the South American Amazon, the water is unusually alkaline because of the driftwood in the water.

If you have fish from this part of the world, a PH of 8 or even higher is healthy. For fish from most other places, a PH of 8 is way too high. Different fish don’t always belong in the same tank – there might be too much of a difference in healthy PH levels for the fish.

How to Safely Lower Your Aquarium’s PH Level

First, you need to buy a testing kit and test the water properly. If you don’t measure the PH precisely, you might treat the water improperly. For example, you might add too much of a PH-lowering chemical to the water, which can kill your fish or you could add too little of the chemical and allow the PH to remain too high.

Testing strips are the easiest way to test your PH. These strips are cheap and reasonably effective.
After buying the strips, dip them in your aquarium and wait for them to change color. Then, compare the color of the strip to a color-coded chart. The color will indicate that the PH is about right, too high, or too low.

Some test strips can also detect other problems with your water. There might be too much iron, ammonia, or nitrate in your water. A test strip kit might have tests for six or nine different factors.
You can also buy test meters, which are better than test strips because they work right away and are more accurate.

A test meter instantly gives you an accurate PH rating, and it might also give you other information. The only disadvantage of test meters is that they cost more in the short run than test strips. You might also need strips if you want to test for something that your meter doesn’t measure.

After you know what the PH is, there are many ways to lower it. Follow the instructions and don’t overdo it. Don’t add any more of a PH-lowering solution to your water than is recommended. Don’t add any more than what is recommended for your tank’s volume or for how high the PH is.

Peat Moss Can Lower Your PH

There are many ways of naturally lowering your tank’s PH without using chemicals. Just because a method is natural doesn’t mean it is completely safe, so you have to be careful.

Know a little bit about each method you use and don’t use a lot more than the recommended amount. Overusing some methods will crash your tank’s PH and make the water slightly acidic, which can hurt or kill your fish.

Peat moss in Aquarium
Peat moss in Aquarium

Peat Moss

Peat Moss is one of the best and safest natural methods you can use. As well as lowering your tank’s PH, peat moss can cleanse your water of contaminants. Peat Moss works by releasing tannic acid and gallic acid into your tank. These gentle acids are a safe way to lower the water’s PH.

Since it takes time for the Peat Moss to release the acid, you need to leave it in your tank. Dipping it won’t work – the acid comes out slowly.

One disadvantage of peat moss is that it can make your tank’s water turn yellow or brown. This discoloration is harmless, but everyone wants their aquarium to look great. Discolored water can ruin the appearance of the tank.

If you leave your peat moss in a bucket for a few days before introducing it into your aquarium, it probably won’t discolor your water. The peat moss will still work to lower your tank’s PH even if you pre-treat it in a separate bucket. Again, the peat moss releases acid slowly.

Some peat moss is of higher quality than other peat moss. Higher quality moss will raise the PH more than lower quality moss. Be careful with the peat moss if you aren’t sure how potent it is.

Another advantage of peat moss is that it can reduce the water’s hardness. If the water in your tank is hard, you may have to use more peat moss to lower the PH. Water hardness can make the peat moss less effective.


Driftwood is another great relatively safe, natural method. It can add to the aesthetics of your tank while serving a practical purpose.

Driftwood gradually releases tannins, which lower PH. It works the same way as peat moss does by releasing a relatively weak, natural acid. Like peat moss, it can sometimes discolor your water, at least temporarily.

While adding driftwood is usually safe, some types of driftwood are worse than others. Driftwood that is good for a tank with reptiles might be terrible for a tank with fish.

Find out a little bit about the type of driftwood you are buying. There may be some chemicals in it that are harmful to some types of fish. You don’t have to be paranoid but do some brief research into the type of wood you are using.

Driftwood can make your tank into a work of art and not merely an average aquarium. Place driftwood in your tank alongside the right plants and fish to create a color scheme that makes your tank look a lot better than average.

Catappa Leaves

Catappa Leaves might be the best, safest natural method. Nothing is entirely safe – things that lower the PH can lower the PH too much if you overuse them. However, catappa leaves are gentle while still being effective.

The leaves have to start to decay before they release their PH lowering acids. Having decaying leaves in your tank isn’t bad for your fish. In fact, catappa leaves have antibacterial properties, so they can treat and prevent certain health problems your fish might have.

Some people might not like the look of dead leaves in their tank. In that case, let the leaves decay in a container of water, and then pour the water into your tank. The water will have PH-lowering and antibacterial properties.

Like driftwood and peat moss, catappa leaves can discolor your tank. However, some people prefer the color that catappa leaves create. Depending on what fish and plants you have in your tank, the color can make your aquarium look more natural and better.

Reverse Osmosis in a Fish Tank
Reverse Osmosis in a Fish Tank

Reverse Osmosis Devices

One of the most reliably effective, although not one of the cheapest ways to lower your tank’s PH is to use a reverse osmosis filter. Reverse osmosis is a process where the filter only allows very small molecules to pass through.

While water molecules are tiny, other molecules are often much bigger. If the filter catches impurities but H20 molecules pass through, the tank becomes closer to pure H20 over time. Pure H20 has a neutral PH, neither too acidic nor too alkaline for fish.

Reverse osmosis filters not only stabilize the PH but remove toxins that can be even more harmful to your fish and plants. Aquarium water can contain traces of heavy metals, pesticides, and arenic. Using a reverse osmosis filter will keep your tank as healthy as possible.

Not every filter is just as good as every other. Good reverse osmosis filters are expensive – a few hundred dollars. Be careful if you are buying a cheap reverse osmosis filter because not all of them are of good quality.


Chemicals are not necessarily harmful and can be a quick way of lowering the PH significantly. Companies sell many chemical solutions that soften your water or lower the PH.

Some use tannins extracted from natural materials, others use diluted synthetic acids. Be at least as careful with solutions as you are with natural materials. Read the label and don’t use any more than directed.

Will high pH kill fish?

Will high pH kill fish? Yes. The pH value determines the environment’s vitality and capability to support aquatic life. The optimal pH level of water where different species of fish can feed, grow, and reproduce is between pH 6.5 – 9.0. If the pH level of water is high or above 9.0, the water or environment becomes alkaline or basic.

Basic water increases the solubility of compounds and elements allowing high levels of carbon dioxide (CO2), toxic ammonia (NH3) and cyanobacterial toxins to be easily absorbed by the fish which greatly affects their reproduction and growth.

Eventually, high alkalinity or high pH can kill fish. Meanwhile, a pH that comes lower than 6.5 can also cause severe harm to fish due to high levels of hydrogen ions that make the water acidic. At this stage, fish’s skin has the tendency to burn, fish cannot reproduce, and fish eggs cannot hatch due to the lack of nutrients hindered by the acidic environment.

Using vinegar to lower pH in an aquarium
Using vinegar to lower pH in an aquarium

Enough Amount of Vinegar to Lower pH of Fish Tank

Pets always have a special place in every owner’s heart. For people who have fish at home, providing them shelter is not enough. Fishes, among any other pets, require extra care for them to be healthy. Changing the water is essential for unbalanced water conditions and too high a pH level in the water can harm the fish.

One of the ways to balance the pH level for the fishes to live is by adding vinegar in the fish tank. Adding white vinegar can lower the pH in the water.

Adding a teaspoon of white vinegar into a 10-gallon tank capacity can greatly help but the vinegar shouldn’t be added directly to the tank for the abrupt change can harm the fish. The acetic acid component of the vinegar when combined with the oxygen in the tank will be converted into carbon dioxide which helps in reducing the pH level of the water.

Change the Water

Changing the water doesn’t require you to buy anything and is effective immediately. Take much or most of the water out of your fish tank and replace it with fresh water.

Most tap water is neutral (PH 7) or slightly alkaline (above 7, but still in the healthy range) and is good for your fish. The best thing about changing the water is that it works right away. You won’t have to wait for the chemicals to take effect.

It is normal for the PH in an aquarium to rise over time. As water evaporates, the water that is left becomes more alkaline. Change the water periodically to keep the PH neutral, don’t use chemicals to lower the PH when the cause is evaporation.

Aquarium C02 reactor
Aquarium C02 reactor

Get a C02 Reactor

For the most part, C02 reactors are to help your plants by providing them with carbon dioxide. They are not really intended to affect the PH of your tank. However, they do make the water in your tank slightly acidic. C02 is a mild acid and will prevent your tank from getting too alkaline.

Sometimes, you can even see oxygen bubbles floating up from your plants. If your plants are receiving a lot of C02, they will produce a lot of oxygen. Sometimes, they produce so much oxygen that you will see air bubbles come up from your plants!

Be Careful When You Lower the PH

Sometimes, mismanaging and excessively correcting the PH in your tank can be worse than ignoring a PH problem. If you pour too much solution into your tank, you might kill all of your fish. You should usually reduce the PH a little at a time.

Only use a quarter of the amount necessary to neutralize your PH the first day. Add another quarter after a day or two, giving your fish some time to adjust to the change. Remember that your PH can go a little too high for a while without harming your fish. You can do more harm than good if you aren’t careful.

Your PH Level Doesn’t Have to be Perfect

It is fine for the PH level to fluctuate a little as long as it remains within a safe range. It doesn’t have to be exactly 7.0 or whatever the ideal PH for the fish you have is.

Fish can handle small fluctuations, some fish can handle larger fluctuations than others. For example, anywhere from 6.6 to 7.4 might be healthy, depending on what fish you have. Sometimes, anywhere from 6.2 to 7.8 might be fine for your fish. If your PH increases from 7.0 to 7.3, you might not do anything. Simply keep your eye on the PH in case it continues to rise.

Rapid changes in PH can also stress your fish out. Correcting the PH every time it swings a little in either direction isn’t the right way to go. Your fish can adjust to small and slow changes.

Why is my PH so High in my Aquarium?

It is normal for the PH in your tank to slowly increase over time if you don’t change the water. When water evaporates, it leaves alkaline substances behind, raising the PH. You aren’t necessarily doing anything wrong if the PH is increasing. It is normal for the PH to increase.

Make sure you change the water once in a while. If this is not enough, use a filter, natural substances, or chemicals to treat the water.

Substrate Can Raise PH

When you add substrate (sand, rocks) to your tank, the PH might increase depending on what you add. Some rocks do not affect the PH, but others do. Make sure the substrate you buy is inert and won’t move the PH in either direction.

Plants Can Raise PH

Some plants can gradually raise the PH in your tank over time. Carbon dioxide and nitrates both make the water more acidic. Plants use up carbon dioxide and nitrates, making the water more alkaline.

You Can Keep Your Fish Healthy

Keeping the PH level healthy for your fish is not usually a hassle. The easiest way to make sure your tank stays healthy is to use a PH meter. Meters are accurate, not very expensive, and quick to use.
If the PH moves out of the healthy range for the fish you have, you should take action.

Be gentle and careful with whatever treatment you use. High PH won’t kill your fish right away, but suddenly making the PH far too low will.

About Rencel Leyran