4 Symptoms Of Low pH In Fish Tank (& How To Test)

Do your fish look unhealthy? Or, for some reason, they don’t seem as happy as they used to be? There could be a number of factors at play, one of them being the PH of their fish tank. Do you know what the symptoms of low PH in fish tanks are?

A variation in the PH levels when they are too high or too low can create serious issues that could be lethal to your fish. A PH level below 6 can be fatal to most fish. It is important to understand the symptoms of unhealthy PH levels, the devices used to measure it, and what the solutions are.

In this article, we will discuss the signs of low PH in fish tanks that will help you catch this issue early, as well as the main causes and how the issue can be tackled and prevented. This information could save you from a lot of work and stress, so keep reading.

Causes Of Low pH In A Fish Tank

The PH level of any fish tank can become low due to a number of reasons. Some of the most common causes include:

Faulty Filtration System

Your filtration system’s primary responsibility is to maintain a healthy environment for the fish. Any fault in this piece of equipment could produce consequences that lower the PH of your aquarium. If you’ve had the same system for an extended period of time and your fish are exhibiting symptoms (which will be discussed later on), consider buying a new one.

Lack of Plants

Plants act as natural absorbers of many chemicals that can lower the PH of an aquarium. When deciding which plants to get, it is usually recommended to consult the local pet store, as some plants are not as effective at lowering PH, and some won’t even make a difference.

Too Many Fish

If you’ve decided to introduce more fish into your aquarium, keep in mind that there’s going to be more wastage at the bottom of your tank. This waste is often a source of Ammonia and Nitrate, which can contribute to lowering the PH in your aquarium.

Decorative aquarium

Lack of Calcium and Alkalinity

Calcium and other alkaline compounds are essential in maintaining a healthy equilibrium, including all the other factors mentioned above, such as waste management. If the quantities of said compounds are in a deficit, your aquarium could soon be faced with symptoms of low PH.

Source of Water

Your source of water should be tested beforehand to determine if it is suitable for use in a fish tank. Sometimes your tap water can be acidic, and if that is acidic, it will behave similarly within the tank, lowering the total PH.

Materials within the Tank

If you introduce other materials into the water, keep in mind that they could also lower the PH. This could be bogwood, Catappa leaves (for shrimp,) peat, Blackwater extract, some planting soils, or any other botanicals like oak leaves.

Symptoms of Low pH in a Fish Tank

Let us take a look at some of the main signs of low pH that you need to look out for:

Algae Growth

Algae thrive in low PH waters, so if you’re noticing a spurt in Algae growth in your fish tank since the last time you cleaned your aquarium or if it’s beginning to falter vision from the outside and the inside, maybe it’s time to consider that your tank may be running on a low PH.

Stressed Fish

This is an obvious one, as your fish are the primary component of your aquarium. If they seem to be stressed or irritated and are generally staying at the bottom of the tank or swimming to the top, it may be an indication that they are struggling to breathe. This is a common sign of a deviation from a healthy pH.

Pale Fish

When the PH levels drop, the metabolism of the fish drops, depending on its species. This can cause the onset of a condition called Autophagy, where the organism begins to break down the cells of the host. As a result, the fish may begin to look paler than usual. This usually indicates that something isn’t right.

Dirt Buildup at the Bottom of the Tank

Fish eat fish food and excrete waste, causing the waste to sink and gather at the bottom of the tank. This waste then starts to appear sluggish and almost dirt-like. It can cause the release of ammonia and nitrate within the tank. This is also something to keep an eye out for.

How To Test & Monitor pH In A Fish Tank

Aquarium pH Testing Kits

There are a variety of test kits available both for freshwater and saltwater PH levels due to confined ranges within which fish can remain healthy. They can be a hassle to use if you have a combination of both within the same tank. They can, however, get the job done if you’re short on resources or if your combination of fish isn’t that diverse.

pH Test Paper

This is commonly known as litmus paper, which you can probably recall from science class. It offers a broad range of PH testing and changes color according to how acidic or alkaline the water within the tank is. But the trade-off is that even though it offers a larger range, it isn’t as accurate.

So, even if it did tell you whether the water is alkaline or acidic, you’re still left with the question of ‘how alkaline?’ or ‘how acidic?’

Hydrion pH Paper

This measurement scale provides the same large range but is slightly more accurate in the sense that it shows the actual PH in increments of 1. The downside is that it does not show further decimal points.

This can be a problem when you’re trying to get the PH exactly right. This is a good solution when your fish are clearly uncomfortable, and you want a quick and easy answer to whether or not you should take action.

Digital pH Meter

This is the best solution as it provides the most accurate reading of the water in the tank. And it is also the most expensive one. However, it breaks the PH down to the level of 0.1, which is all the information you need to understand what is happening in your fish tank.

This also serves to make your aquarium the perfect simulation for perfect growth. This is generally only recommended for serious fish keepers who are usually breeding fish to sell.

Apera Instruments pH Pen

When it comes to getting the most out of your money, this is the best option, according to the general consensus on the market. Not only does it come for a lesser price than the digital pH meter, but it also provides accurate readings and is designed specifically for the purpose of affordability.

If you’re looking for the one that most people recommend, go for this one, and you won’t go wrong.

How to Check Your Tank’s pH Levels

Strip Tube Kit

If you have a strip tube kit, put the kit directly into the water and then compare it to the reference chart that comes with it. Another advantage is that they generally come with other specific color indicators for the presence of Ammonia and Nitrate. This can be beneficial as it breaks down the cause even further in case you discover a problem. 

Test Tube Kit

In the case of a test tube kit, scoop up a vial of water from the tank and then shake it to see if the reading begins to change. Use the reading to reference from the manual what the PH levels are. Make sure your hands are clean beforehand, or you might get the wrong answer.

How Often Should You Check Your PH Levels?

Fish experts generally recommend checking the PH level of your tank at least once a week and a glance or two a day to ensure that your tank and the fish are not exhibiting the symptoms mentioned above.

It is also recommended that you keep the nitrate and ammonia levels in check, as they are also relatively important for the well-being of your fish.

How Do I Raise My Ph In My Fish Tank?

Add Crushed Corals to Your Aquarium

Adding crushed corals is a good solution since they contain a high concentration of calcium carbonate, which is high in alkalinity. It could help to raise the PH of your aquarium as they settle in the water.

There are a couple of ways to introduce crushed corals into the tank. You could simply add them to the bottom of the tank, or you could add smooth crushed corals to your aquarium’s filter so that the water is refreshed every time a cleaning process is initiated.


Adding limestone to your aquarium serves the same function as the crushed corals, as it is also high in calcium carbonate. Not only is it good for maintaining a healthy PH, but it is also aesthetically pleasing. Plus, it is widely available, and you can find it at a relatively low cost.

Experts recommend the ‘Texas Holy Rock’ for this purpose. Just make sure not to overdo it so you don’t end up having to solve the problem the other way around.

Dolomite Chippings

Dolomite chippings are composed of a high concentration of calcium and magnesium. Both of these are suitable compounds for raising the PH levels in your fish tank.

If you feel like your aquarium is lacking in visual appeal, these chippings may also help change that. It is also considered to be a faster solution than the previous two that have been mentioned.

Aeration of the Tank

Exposing the fish tank to more oxygen will help to dilute the concentration of carbon dioxide within the water and will help to alleviate lower PH levels within the tank.

The production of carbonic acid occurs when carbon dioxide dissolves in water and can severely lower PH levels. This is also an immediately effective solution as nothing else is required for this particular option.

Baking Soda

You can add baking soda into the fish tank depending on how much of an increase you want in PH levels. Be careful not to add too much as that could cause unhealthy increases in PH levels and may create a hostile environment for the fish.

Regularly check the PH levels of the water to ensure that you are adding the desired amount, not too little or too less.

Boil Your Driftwood

If you’re using driftwood in your fish tank, know that when driftwood interacts with water, it produces a lot of tannic acids and can lower the PH levels within your aquarium. You might want to replace them with some other sort of decoration, but if you really want to keep the driftwood, boiling it regularly will help to keep the PH regulated.

This YouTube video explains how to do it – https://www.youtube.com/watch?v=qHlsvNIGTRM

Check Out The E-Books!

For a limited time, only you can get both The Complete Guide On Caring For Betta Fish & The Ultimate Betta Tank Mate Guide for just $14.99!

Find Out More Here!

This image has an empty alt attribute; its file name is Bundle-2-e1661845950782-1024x720.png


Can Fish Die From Low pH?

A low PH produces unsuitable living conditions for any fish, just as acid rain causes fish to die in other water bodies. The same can happen in your aquarium, and at a PH level below 6, it can be a cause for serious alarm with possibly fatal consequences.


Now you know the possible causes and symptoms of low PH in a fish tank. You have also been equipped with solutions for when the problem does occur and methods to ensure its prevention.

Remember, keeping the PH of your fish tank within a healthy range is essential. Any major deviation can quickly create problems for the fish. Use the links provided to expand your knowledge and keep in regular touch with your local pet store, as they are usually quite knowledgeable.

The best indicators are generally the fish themselves, as they are the main highlight of your aquarium. Any changes in their behavior should be noticed and may be linked to a possible cause. So, you should regularly keep a check on their well-being.