How To Lower The pH In A Freshwater Aquarium


Share This Post

The preferred way to lower the pH in freshwater aquariums is to use natural methods such as adding peat moss, driftwood, and catappa leaves. However, other solutions such as using carbon dioxide (CO2) reactors and reverse osmosis are also commonly used. 

Are your pH levels too high inside your freshwater aquarium? If so, you have come to the right place! 

When taking care of your freshwater aquarium, you are probably aware there are a few factors to consider, but the most important is keeping the pH inside your aquarium stable. To keep your fish happy and healthy, you must maintain pH levels by frequently monitoring and testing the water quality.

What Is The “Ideal” pH For Freshwater Aquariums?

The pH scale ranges from 0-14. If water has a pH <7.0, it is acidic, and if it is >7.0, it is considered alkaline (or a base). Water that has a pH of 7.0, is considered neutral, which is what most “pure water” is measured as. 

The most common question asked by aquarium hobbyists is, what should the pH of the water be when keeping fish. The answer is not so simple, as no pH applies to all breeds of fish. This is because fish have a very diverse habitat; some fish originate from the ocean, some from rivers, and some from brackish conditions, which is somewhat in between the two in terms of salinty. 

However, generally, freshwater fish love water that has a pH between 5.5 and 7.5, while saltwater fish prefer slightly alkaline conditions.

5 Ways To Lower The pH In Your Freshwater Aquarium

If you have already checked the pH level and find it higher than your fish’s recommended level, do not worry. We have listed a few possible ways to lower the pH of your aquarium water safely, so that it reaches the optimal level and stays consistent.

We always recommend using natural methods first when altering pH levels inside your freshwater aquarium. Often, using store-bought chemicals can change the pH levels drastically, which is likely to stress your fish and make them sick. 

1. Peat Moss

A wonderful natural way to safely lower the pH inside your freshwater aquarium is peat moss, which filters contaminants in your water. The tannic and gallic acids the peat moss releases, attacks bicarbonates in the aquarium water, lowering the pH and reducing the water hardness. 

The only downside to using peat moss is sometimes it discolors the aquarium water, however, this will soon clear up. Some hobbyists like this “natural tea-look” but, if you have some guests coming over and do not want your aquarium water discolored, you can pre-treat water in a separate container a few days before adding it into your aquarium. 

To effectively use peat moss to lower the pH, it must stay in your aquarium, as dipping it in now and then will not work.

The easiest way to use peat moss is to buy pellets or chunks that you add to your aquarium filter. Unfortunately, there are still no exact dosage instructions, therefore, we recommend you start with a small piece and monitor the pH (with pH strips or a pH meter), adding more if needed. 

Peat moss is also regularly used before adding plants and fish into aquariums to get the water chemistry under control. 

2. Driftwood

Driftwood is naturally found in a fish’s wild habitat, so not only does it create an awesome look, but it will also make your fish feel right at home!

Driftwood releases tannin, which can reduce the pH inside your aquarium. Like peat moss, adding driftwood will discolor the water, which is a natural process and will not stress your fish or harm any plants. 

Before adding any driftwood, it is important to check it is aquarium-safe, as not all driftwood is safe for freshwater aquariums. We recommend taking extra precautions, just in case! Once you have your piece of driftwood, it is recommended you boil it in salt water to sterilize it. This ensures there is no dirt, fungi, or debris on the wood, and also helps prevent it from discoloring the aquarium water. 

3. Catappa (Indian Almond) Leaves

Indian Almond (Terminalia catappa) leaves are a popular way to lower pH in aquariums, and are increasingly common in pet stores worldwide, so, you will have no trouble getting your hands on some! 

Just like using driftwood and peat moss, catappa leaves slowly release tannins as they decay in the water. In addition to their pH lowering capabilities, it is thought they also contain antibacterial properties, which can help treat fin rot in fry (baby fish). 

You can simply place the Indian almond leaves loosely in the water. The water flow will carry them around the aquarium as they decompose, creating little “magic carpets” for any invertebrates to hop on for a ride. 

If you prefer a tidy aquarium, you can bunch them up using string and place them in the filter, out of sight. If you want to avoid adding them into your aquarium completely, you can add some leaves combined with some aquarium water into a separate container, and pour it in when you perform your water changes. 

Indian almond leaves are popular, due to their more-precise dosing measurements. It is estimated that one leaf per 10 gallons of water is plenty to see a gentle difference in lowering the pH. 

4. Reverse Osmosis (RO)

A more expensive choice, yet, a very precise way to adjust the pH inside your freshwater aquarium, is to use reverse osmosis (RO) water. The RO water has a semipermeable membrane that purifies the water. This specialized membrane filters out approximately 90-99% of water impurities that could be the cause of increasing your aquarium water’s pH. 

The downside to this method is the price and maintenance required. 

Installing an RO unit can cost hundreds of dollars. However, it is a natural deionization process that will not stain your aquarium water yellow, and it is suitable for long-term use, making it a fantastic choice if you have a constant supply of hard tap water in your home. 

5. Carbon Dioxide (CO2) Reactors

If you have a lot of live plants in your freshwater aquarium, it may be worthwhile to invest in a CO2 reactor. 

Carbon dioxide reactors provide the aquarium water with a constant flow of CO2, which is vital for your plants to grow. As CO2 is slightly acidic, it can help lower the pH inside your aquarium, as long as you keep a reactor running. 

To keep an eye on carbon dioxide and oxygen (O2) levels inside your aquarium, it is recommended you get yourself a CO2 sensor and an O2 sensor

Whichever option you decide, it is important to lower the pH in your freshwater aquarium gradually and test the water before and after with a pH probe/sensor or pH testing strips. 

Now, if you have lowered the pH too much, do not panic – we have some tips on how to safely raise the pH just for you.


When caring for fish inside a freshwater aquarium, it is essential to maintain water chemistry, including pH. Keeping the pH stable inside an aquarium can often be challenging at times, and sometimes you may need to lower or raise the pH. 

Adding peat moss, driftwood, and Indian almond leaves, are a great way to naturally lower the pH inside aquariums, keeping your fish happy and healthy. Other methods such as using RO units and CO2 reactors are also efficient ways to lower pH in aquariums. 

If you have any questions regarding pH, or what pH sensor would best suit your testing needs, please do not hesitate to contact the world-class team at Atlas Scientific, we are always happy to help! 

Sensors & Devices

Subscribe To Our Newsletter

Get product updates and learn from the best!

More To Explore


Analog Vs. Digital Sensors: Understanding The Key Differences

One of the key differences between analog and digital sensors is their output resolution. For example, analog sensors provide infinite resolution since they provide a continuous range of values, while digital sensors have a finite resolution determined by the number of bits used to represent the signal. Another difference is the susceptibility to noise. Analog


Hydroponics Pros And Cons Explained

Pros of hydroponics include efficient water use, faster growth rates, and the ability to grow crops in limited spaces. However, cons may involve higher initial setup costs, the need for technical expertise, and a reliance on artificial lighting and climate control. Also, many argue that hydroponically grown produce may lack certain flavors or nutrients compared

Want to learn more about our products?

Scroll to Top

To track your order please enter your Order ID in the box below and press the "Track" button. This was given to you on your receipt and in the confirmation email you should have received.