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Why are my aquarium plants turning brown?



Aquarium plants turning brown can be a distressing sight for any aquarist. Understanding the potential causes behind this is crucial for remedying the situation and restoring the health of your aquatic plants, as brown leaves or stems are often indicative of underlying issues within the aquarium environment. Here are a number of possible reasons why your aquarium plants may be going brown and are no longer as healthy as they should be.


You may not have true aquatic plants

The first thing to check when your plants start to turn brown is whether they are true aquarium plants - able to survive and grow underwater. There are many aquarium stores that sell attractive non-aquatic plants to unsuspecting beginner aquarists. Some common examples of this include Aluminium plant (Pilea cadierei) and Purple waffle (Strobilanthes alternata) among others. These plants will start to go brown, drop leaves and die off after just a few weeks of being submerged in your aquarium. If this is the case, it is best to remove these from your aquarium before they disintegrate. FloraPhyta only sells true aquatic plant species, able to survive and thrive in your aquarium. If buying plants elsewhere, ensure you research the plants you are buying beforehand.


Emersed grown plants

Many aquarium plants that are sold in the aquarium industry are grown in their out of water form (emersed). Emersed plant are sturdier, ship better, and are more resilient when adjusting to your aquarium. When these plants are submerged in your aquarium they quickly adapt to the new conditions. To do this, they transition to their underwater (submersed) form. As this transition happens, the old leaves may turn brown and fall off, as the plant simultaneously grows new leaves that should be healthy and green. This is a completely normal and essential process and as long as they are provided with everything they need the plants will recover and grow to their full potential.


Insufficient light

Lighting is another cause of aquarium plants turning brown and dying. Adequate light is essential for all plants to be able to photosynthesise (a process in which they convert light energy into chemical energy to fuel their growth) and grow, without it their lower leaves may begin to turn brown. If your plants look somewhat 'leggy', with long internodes, this may be your reason. Different aquatic plant species have different light requirements, some require high lighting, others low lighting, and some will grow in a range of light levels. This means it is important to ensure your aquarium lighting matches the requirements of the specific plants you want to keep. The depth of the aquarium will also influence this, plants growing on the bottom of the tank will receive much less light than those floating on the surface. If your aquarium plants are turning brown and you think lighting may be responsible, try increasing the hours of light or consider upgrading your aquarium lights or switching out your high light plants for low light species instead. Find out more about how much light your aquarium plants need here.


Algae issues

Conversely, too much light or nutrients can be the cause of algae overgrowth that can contribute to the browning of aquarium plant leaves. Brown Algae (Diatom algae) appears as a slimy coating on aquarium surfaces, including plant leaves. They are especially noticable on slower growing species and can quickly cover plant leaves, causing them to appear brown or discoloured. Algae thrive in conditions where there is an excess of nutrients and light, outcompeting plants for resources and growing over their leaves. This shading can limit the amount of light reaching the plants, hindering their ability to photosynthesise effectively. Controlling algae growth is best done through reducing the lighting period on your aquarium and regular water changes.


Nutrient imbalances, deficiencies and overdose

All plants, including aquatic plants, require a number of nutrients to thrive. These include macronutrients such as nitrogen, phosphorus, and potassium, as well as micronutrients like iron, manganese, and zinc. When there are not enough of some of these nutrients symptoms will show up in your plants, including the leaves turning brown. The main culprits for plants turning brown in regards to nutrient imbalances are nitrogen deficiency, potassium deficiency, iron overdose, and phosphate overdose or deficiency.


Root issues

Problems with the plant's root system, such as root rot or inadequate oxygenation, can impair nutrient uptake and contribute to browning leaves. If you notice bubbles rising from the substrate when disturbed, along with a distinct sulfur smell, it's indicative of anaerobic conditions in the substrate. While not all species are equally impacted by this, regular gravel vacuuming is recommended to mitigate any issues. Ensure your plants have a healthy root system by providing suitable substrate, adequate aeration, and avoiding overcrowding. Trim any damaged or decaying roots and replant affected plants as necessary.


CO2 deficiency

The final potential cause of aquarium plants turning brown is a lack of carbon dioxide (CO2). Plants require sufficient levels of CO2 in order to photosynthesise and grow. When there’s insufficient CO2 in the water, plants can’t photosynthesise effectively. This can lead to a lack of energy, causing the plants to become stressed and unhealthy. As a result, the leaves may turn brown, a common symptom of plant stress. If your plants also appear stunted and aren't growing, this may be your issue. Different plants require different levels of CO2, some species will only grow in the aquarium if additional CO2 is consistently added, others are much easier to grow and will do so without the addition of CO2. It is important therefore, to ensure your aquatic plants are suited to your particular aquarium. You can find a list of low light/low tech (no CO2 required) plants here.


By understanding the potential causes of why your aquarium plants are turning brown and making the necessary adjustments, you can help your plants regain their health. Remember, every aquarium is unique, so it may take some time and experimentation to figure out what works best for your plants.

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