Why Are My Aquarium Plants Turning Brown? Learn to Overcome

I am a fan of planted aquariums and started my first planted tank back in 2013. They can bring the visual appeal of your aquarium to a level that no other item can do.

I must admit keeping live plants is relatively more challenging than just keeping fish from my own experience. But I never gave up. I was in love with the greenery, and I learned how to maintain them with experience, study, and research.

I often receive a common question on different platforms; why are my aquarium plants turning brown? Aquarium plants are sensitive to water conditions. If the tank water condition deteriorates, plants show the first warning sign that things started going wrong!

Plants need a balanced combination of light, CO2, and other nutrients. Below are the main causes for aquarium plants to turn brown.

• Lack of necessary nutrients
• Improper lighting
• CO₂ Deficiency
• Presence of brown algae
• Improper substrate
• Poor water condition
• Wrong way of planting

The primary reason for aquarium plants turning brown

When plants start turning brown, it’s an indication of their sickness and nutrition deficiency. Plants need light and CO2 for the photosynthesis process, which is crucial for their growth and survival.

Photosynthesis is a photochemical reaction that takes place in a plant’s green leaves. Through this process, from light and CO2, plants produce sugar and oxygen, which become the source of energy for their survival.

Other nutrients such as nitrogen, phosphate, potassium, magnesium, iron, and manganese are also essential for aquarium plants’ healthy living. Plants collect these nutrients from the aquarium water and substrate primarily through their leaves and roots.

A balanced supply of all the above elements is the key to having healthy plants. Any irregularity (deficiency or surplus) can cause plants to turn pale and brown. I’ll discuss it all one by one.

1) Inadequate lighting

As I said before, lighting is one of the basic needs of a plant’s survival. It’s the source of their energy. As we take carbohydrates from food, plants make sugar from photosynthesis. If the light is deficient, plants will definitely suffer from starvation. 

Different aquarium plants have different levels of lighting needs. Typically fast-growing plants require more energy to grow, hence requiring intense lighting.

Slow-growing plants like Anubias, Java Fern, Marimo Ball, etc., require less. But more or less, all aquarium plants need light. And if it is inadequate, they will suffer from vitality and vigor, resulting in turning brown to death. 

Insufficient light symptoms:

1. Plant growth becomes slow or has no growth at all. 
2. Mature leaves turn yellow or brown.
3. The whole plant turns pale, white, or transparent. 

Mitigation for insufficient lighting:

• Ensure full-spectrum lighting:

Plants get sunlight in the wild, but indoor aquariums are limited to sunlight exposure. Whereas direct sunlight for aquariums is not advisable as it promotes uncontrolled algae growth. A full-spectrum lighting system is the best solution to provide sufficient light for planted tanks.

• Use efficient LED lights:

Nowadays, LED aquarium lights are readily available in the market. LED lights are reliable and cheaper. As long as they are providing the necessary spectrum, plants will thrive.

• Know your plant’s needs:

As I said before, the level of need for each plant is not equal. You have to know the requirement of your plant. But in general, 1.5 watts of LED lighting per gallon are the minimum requirement for planted tanks with low-light plants. For high-light-demanding plants, the condition is 3 watts of light per gallon.

• Keep low-light-demanding plants:

Though your option of choosing plants will shrink by this, low-light plants are hardy and more comfortable to keep. If you are a beginner, I’ll suggest keeping low-light plants (like Anubias, Java Fern, Java Moss, Marimo Ball, Dwarf Rotala, etc.)

2) CO2 deficiency

Then it comes to CO2, which is another essential element for the photosynthesis process. So plants will suffer from the same consequence of light deficiency. CO2 naturally is present in aquarium water to a certain level.

Low-light plants can do well with the naturally occurring CO2 of aquarium water. But if your aquarium is densely packed with lots of demanding plants, CO2 may become limiting, and plants suffer from starvation. They turn brown and pale to death.

CO2 deficiency symptoms:

1. Diminutive plant growth. 
2. Leaves turn brown and yellow. 
3. Stems become brown leading to plant death.  

CO2 deficiency mitigation:

• Select low-demanding plants:

The CO2 requirement of the plant is directly related to its light needs. So, if you select low-light plants, they will consume less CO2.

• Maintain a day/night cycle:

Plants consume CO2 in the presence of light and produce sugar and oxygen. But in darkness, they reproduce CO2 from oxygen and sugar by respiration.

Keeping lights off at night helps to develop CO2 levels from fish and plant respiration.

• Use a CO2 injection system:

By adding CO2 to the tank water, you can increase the CO2 level. You have to install a CO2 system for injecting CO2 into the aquarium eater.

A standard CO2 injection system consists of a CO2 bottle, CO2 regulator, diffuser, bubble counter, needle valve, and a few other optional accessories.

• Reduce the water circulation flow:

If the tank water circulation current is too high and forms many bubbles, dissolved CO2 evaporates from the water. So, reducing the turbulence of aquarium water is another way to keep CO2 dissolved in the water.

Risks associated with high CO2 level

High CO2 levels in aquarium water can be fatal for your fish. So, especially if you are using a CO2 supplementation system, controlling the dosing rate is crucial.

Very high-demanding plants do well at a CO2 level of 30 mg/l. But the safe level for fish is below 35 mg/l of dissolved CO2. Beyond this, fish start showing signs of stress and lethargy. They lose their appetite, become weak, and may die.

3) Other Nutrients Deficiency

Besides light and CO2, there are some essential nutrients for plants that help them grow and be healthy. Aquarium plants collect these nutrients from the tank water and substrate.

Some of these nutrients are macronutrients, and plants require them plenty. Nitrogen, Phosphate, Potassium, and Magnesium are macronutrients.

Plants need some amount of Iron and Manganese also, and they are micronutrients. They require a balanced amount of macronutrients and micronutrients. Deficiency and surplus of nutrients both can cause problems.

Nitrogen

Nitrogen is a vital nutrient for all kinds of plants, including your aquarium greenery. Aquarium plants collect nitrogen in the form of nitrate, nitrite, and ammonia compounds. Thus, they reduce nitrate, nitrite, and ammonia from the aquarium water and make a healthy fish condition. 

In a fully cycled tank, ideally, no ammonia and nitrite should be present. So the primary source of nitrogen in aquarium plants is dissolved nitrates in the water. 

Symptoms of nitrogen deficiency

1. New leaves appear curly and reddish. 
2. Mature leaves turn brown.
3. Leaves start falling off.
4. Slow growth.  

Excess nitrate and ammonia

Nitrogen compounds are essential for plant growth, but they are toxic for fish. If ammonia builds up in a tank, it indicates the tank is not fully cycled; or the nitrogen cycle is somehow disturbed.

Nitrate buildup is a common problem in fish tanks, even in planted tanks. If aquarium plants cannot absorb all the produced nitrate, it will rise in level. Water change is the solution for the above cases. Otherwise, it will stress or even kill your fish.

Excess nitrates in the aquarium water can promote algae growth also.

How to overcome nitrogen-related issues

Maintaining a balanced level of nitrates (5-10 mg/l) in planted tanks is the key. If the nitrate level goes down to zero in a cycled tank, it indicates plants are consuming a lot. And they are probably overcrowded. 

To reduce the nitrate level, perform regular water changes. 

Phosphate

Phosphate is an essential nutrient for aquarium plants. Phosphate compounds naturally occur in aquarium water from many sources, like decaying plant matter, fish wastes, and food leftovers.

Prepared fish feed and organic salts also provide phosphate to the tank water. Phosphate deficiency causes several issues for aquarium plants.

Symptoms of phosphate deficiency

1. Holes in the leaves.
2. Brown spots on the leaves.
3. New leaves start turning yellow. 

Symptoms of excess phosphate level

1. Plant leaves start turning deep brown to black.
2. Excess algae start growing in the aquarium water. 

How to overcome phosphate issues

If you observe phosphate deficiency symptoms, add phosphate-rich fertilizer and organic salt to the aquarium water.

For excess phosphate issues, perform water changes and a thorough substrate cleaning.

Related read: Best Fertilizer for providing nutrient to plants

Potassium

Potassium is one of the salient nutrients for plants that naturally occur in aquarium water. Plants consume plenty of potassium to grow and flourish. So, the inadequacy of it stresses them a lot.

Symptoms of potassium deficiency

1. Pinhole starts forming on the leaves. 
2. Edges of the leaves become pale and yellowish. 

How to overcome potassium issues

Maintain a good water condition keeping balance in pH, hardness, and CO2 level. Potassium supplementation is also useful. 

Magnesium

Magnesium is a vital nutrient to maintain your greenery. Magnesium and iron are essential for a plant’s bright green coloration. Whereas magnesium deficiency reduces the plant’s iron absorption capacity. So, they are interlinked.

Symptoms of magnesium deficiency

1. Leaves start turning brown with brown and yellow spots. 

How to overcome magnesium issues

Fertilization and nutrient-rich plant soil can fix this issue.

Iron

Iron is an essential nutrient for the vibrant green color of plants. Iron salts can be present in tap water, but all forms of iron compounds are not soluble. Plants can absorb only soluble iron compounds from the tank water. So iron deficiency is a common issue.

Symptoms of iron deficiency

1. Plant leaves start losing green color and turning pale, yellowish, and colorless.
2. New leaves are grown white and pale. 
3. Leaves and stem tissues turn necrotic leading to death. 

How to overcome iron deficiency

Iron is difficult to absorb from water. So providing a nutrient-rich substrate is the best solution to overcome iron deficiency. 

Manganese

Plants don’t need manganese in too many amounts, but they are important. Mainly, it helps plants’ metabolism to utilize other nutrients effectively and grow.

Symptoms of manganese deficiency

1. Plants become weaker, and their growth slows down.
2. Plant leaves start turning yellow to brown. 
3. Start forming holes in the leaves.

How to overcome manganese deficiency

Iron-rich substrates and fertilizers contain traces of manganese and can supplement it.

Other reasons for aquarium plants turn brown

Brown algae

Sometimes aquarium plants may turn brown due to algae formation. Brown-colored algae can form a layer on green plants. It happens mostly in partially cycled tanks. So lack of nutrients may not always be the reason for a brownish plant.

Brown algae are not so harmful as nutrient deficiency, and the mitigation is relatively more painless. Perform a regular water change. Hopefully, the problem will be resolved.

Poor water condition

Plants can absorb some impurities from the water, but not all. Significantly undissolved pollutants can affect water quality badly. Thus, low water quality can be a significant reason for your plants losing green.

If your tap water contains undissolved iron matter, it can turn plant leaves brownish. Similarly, dirt and debris can cause the same.

Effective mechanical filtration is the key to keeping the tank water free from undissolved solids. Perform regular water changes, which is very beneficial to ensure the health of both fish and plants.

Improper substrate

The substrate is a crucial consideration for a planted tank as most aquarium plants take nutrients from the substrate. A mineral-riched suitable substrate can encourage your plants to prosper.  

Mineral-riched soils are my first preference in planted tanks. But I tried growing plants in gravel, and it works for many plants. Whereas a sandy substrate is not suitable for most aquarium plants. 

If you choose the wrong substrate for the plants, it can be a possible reason for your plants turning brown to die.

Wrong planting

You have heard it ‘as you sow, so shall you reap.’ The way you planted the aquarium plants makes their future foundation for growing healthy.  

Each plant species has a unique technique for plantation. You have to ensure the right way to plant aquarium plants. For instance, some plant roots need to be buried deep in the substrate, while others should not go deep. Some aquatic plants don’t have roots, but some grabbing organs like rhizoids. They also need another particular planting method.  

If the planting is not proper, plants cannot settle and grow; instead, they turn brown and die. 

Other problems associated with aquarium plants

• Holes in leaves

The possible reason for forming holes in the leaves of aquarium plants is potassium and phosphate deficiency. Initially, it creates black dots and then grows visible holes.

• Slow growth

Slow growth can be the consequence of all sorts of deficiencies. Inadequate light, CO2, and improper nutrition can slow down the expected growth of your aquarium plants.

• Brittle leaves

If you observe brittle leaves of your aquarium plants, probably the pH level of the water is too high. Check the pH, and if the value is below 7.5, then the possible reason could be something else.

Iron and potassium deficiency also can cause brittleness of plant leaves.

• Black leaves

Poor water conditions and excess iron contamination in the water can be the culprit for aquarium plant leaves turning black. Water change is the solution to get rid of it.

FAQs

Takeaway

The three critical factors in maintaining your greenery are the lighting, water condition, and substrate. Be conscientious in keeping those things right, and your planted tank will burgeon. Keep in mind the following points: 

• Choose the right plants and arrange sufficient lighting and a suitable substrate for them.
• Regularly perform water tests and water changes. 
• Ensure effective filtration is in place and properly functioning. 
• If you keep high light plants, use CO₂ supplementations, and operate them properly.
• Pick the appropriate type of fertilizer during fertilization. Liquid fertilizer is useful.