Can Aquarium Plants Tolerate A High pH?

Although a pH level of 6.0-7.0 is recommended for planted aquariums, there are a few aquarium plants that can tolerate a higher pH range, due to their origin or adapting to water conditions in captivity.

Growing plants in aquariums are becoming more popular among plant enthusiasts. Adding aquarium plants can enhance the water quality and prevent excessive algae growth, benefiting any fish or corals inside. As fish produce oxygen, keeping plants helps your fish respire and stabilizes pH levels, and as a “thank you”, your fish provide your plants with carbon dioxide from waste. 

When taking care of your planted aquarium, you are probably aware there are a few factors to consider, but the most important is keeping the pH inside your aquarium stable. 

What Is The “Ideal” pH For Planted Aquariums

Most planted aquariums function best with a pH between 6.0 and 7.0 – slightly acidic. However, many plant species are not fussy, and therefore, can grow in more alkaline waters (7.0+), often adapting or tolerating higher pH levels. In aquariums with a high pH, often free ammonia can become more toxic to fish, but plants seem to cope with these conditions. 

With that being said, pH is frequently misunderstood in the aquarium world.  While pH is important, KH (carbonate hardness) and GH (general hardness) are more valuable measurements when assessing the water quality inside your aquarium, particularly for aquarium plants.

What Is Considered A “High pH” In An Aquarium?

The pH scale runs from 0-14; 7 being neutral, <7.0 is acidic (low pH), and >7.0 is alkaline (high pH). While anything over 7.1 is considered alkaline, an aquarium that has a high pH, generally means it is very alkaline. 

When the pH of water increases above 9.0, this would be considered very alkaline. When the pH is greater than 9.0, ammonium is converted into toxic ammonia inside the water, killing your fish and plants. Plants that have ammonia toxicity will form burnt leaves and blackened roots.

Can Aquatic Plants Tolerate High pH Levels Inside An Aquarium?

Adding aquatic plants to your aquarium can affect the pH of the water due to the release of oxygen via respiration, but, the pH can also affect the growth of aquarium plants. Just like corals and fish, aquarium plants are adapted to the water chemistry from their origin. 

Saying that, most aquatic plants in the aquarium trade will grow at a wide range of pH, GH, KH, and TDS (total dissolved solids) if the TDS is not from salts in the aquarium.

Plants That Can Tolerate A High pH

Java Moss (Taxiphyllum barbieri)

• Origin: South-East Asia
• pH: 5.0-8.0
• Carbonate Hardness: 0-21 dKH
• General Hardness: 0-30 dGH

Java Fern (Leptochilus pteropus)

• Origin: South-East Asia 
• pH: 5.0-8.0
• Carbonate Hardness: 0-14 dKH
• General Hardness: 0-30 dGH

Hornwort (Ceratophyllum demersum)

• Origin: Native to all continents apart from Antarctica 
• pH: 6.0-9.0
• Carbonate Hardness: 5-15 dKH
• General Hardness: 5-15 dGH

Amazon Sword (Echinodorus grisebachii)

• Origin: South America 
• pH: 6.5-7.5
• Carbonate Hardness: 3-8 dKH
• General Hardness: 2-12 dGH

Water Wisteria (Hygrophila difformis)

• Origin: Asia, mainly India 
• pH: 6.5-7.5
• Carbonate Hardness: 3-8 dKH
• General Hardness: 3-19 dGH

Anubias (Anubias barteri)

• Origin: West Africa
• pH: 6.5-7.5
• Carbonate Hardness: 3-8 dKH
• General Hardness: 2-15 dGH

What Causes High pH In An Aquarium?

An aquarium can have a high pH from:

• Carbon dioxide depletion. When keeping an aquarium, it is important to understand how CO2 affects pH in water. 
• Regularly adding tap water into your aquarium, and not using a water conditioner. 
• Adding too many alkalinity supplements. 
• Depletion of aquarium plants. 
• Too much fish waste.

How To Lower The pH Inside Your Aquarium

You can safely lower the pH inside your aquarium by:

• Reverse osmosis (RO)
• Carbon dioxide (CO2) reactors
• Adding Indian almond leaves
• Adding driftwood
• Adding peat moss

When lowering the pH in your aquarium, it is also valuable you know the symptoms of low pH in a fish tank. 

So, Will Adding Plants Lower The pH In An Aquarium?

When you add plants to an aquarium, they can increase the pH level of the water due to CO2 uptake. This effect of CO2 removal from aquarium plants is however small, and should not cause large fluctuations in pH levels.

Plants also metabolize other compounds such as nitrogenous substances and ammonia, which is great news for your corals and fish! Once absorbed, the nitrogenous substances can trigger biological processes that create free hydrogen ions in the water, thus lowering the pH. 

Now, you may have heard that decaying plants can also lower the pH inside aquariums. While that is true, it is not recommended, as decaying plants are not safe if you have fish or other aquatic organisms inside your aquarium. 

The Best Way To Monitor pH Levels Inside Aquariums

To accurately monitor pH levels inside your aquarium, a pH probe connected to a pH meter is highly advised. However, there are other methods to monitor pH levels, such as pH paper test strips, known as Litmus paper. 

If you have already got a pH probe and are unsure how to use it, we have you covered here!

As already mentioned, CO2 depletion is a cause of high pH levels inside aquariums, therefore getting yourself a CO2 sensor is also recommended, particularly, if your aquarium is heavily stocked with plants. 

Conclusion

Most aquatic plants can tolerate high pH, however, this depends on their origin. Aquatic plant species found in South-East Asia, India, South America, and West Africa, are known to thrive when pH levels increase above 7.0 (neutral). 

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!

pH Probes & Sensors