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Aquarium Plants Turning Yellow: 10 Reasons And Solutions

Aquarium plants are quite delicate and require a lot of tending. As such, it can be quite harrowing to see them turn yellow even after all the care you put in.

Aquarium plants may turn yellow due to nutritional deficiencies, poor water quality, diseases, or inadequate light.

If not attended to quickly, the plants may turn darker, wilt, and die. Fortunately, you can relieve them of this problem.

In this article, we’ll decipher the different reasons behind yellowing and the corresponding solutions.

Yellow-leaf-in-water

Reasons Why Your Aquarium Plants Are Turning Yellow

Here are some of the things that could be affecting your tank and causing your plants to change color:

1. Nutrient Deficiency

Plants need nutrients to power their biological processes. They cannot survive in the absence of these nutrients.

The first sign that indicates their lack is when plants begin to turn yellow and rot.

If you leave signs of nutrient deficiency unchecked, the symptoms will spread to other parts of the plants and other plants in the tank.

With time the plants will show stunted growth, poor vigor, and reduced yield.

Yellowing-in-plant

Here are common nutrients that plants need and what their absence could spell for your aquarium plants:

a) Nitrogen Deficiency

Plants absorb nitrogen in several forms— nitrates, ammonia, and urea. When the nitrogen level in the tank drops below the optimal range, it can cause the plant to yellow and wilt, especially if they’re older.

In younger plants, nitrogen deficiency cripples the plant’s growth and causes newer leaves to remain small.

b) Potassium Deficiency

Plants that require high potassium levels to grow, like the anubias and java fern, will turn yellow when placed in an environment with lower potassium levels.

Potassium deficiency also causes them to have black spots and holes. That’s one way to distinguish this deficiency from others.

If you don’t correct the potassium deficiency at this point, it may lead to stunted growth.

c) Insufficient Magnesium

Magnesium is a major component of chlorophyll, making it important for photosynthesis. Its absence means that plants cannot produce chlorophyll (which provides green pigmentation).

The veins remain green while the leaves turn yellow and begin to droop.

d) Sulfur Deficiency

Plants with sulfur deficiency start yellowing from the newest leaves before spreading to other parts.

e) Lack of Phosphorus

Phosphorus (like nitrogen) is a macronutrient required for plants to drive a lot of biological functions.

A phosphorus deficiency may cause the leaves to be yellow and give them soggy brown patches called algae spots. This is particularly common in older leaves.

f) Iron Deficiency

Aquarium plants require traces of iron to produce chlorophyll and for optimal growth. Plants with iron deficiency cannot produce chlorophyll and will turn yellow as a result.

As the deficiency persists, the color changes from yellow to white and ultimately black.

How to Identify The Nutrient Deficiency In Your Tank?

Different nutrients move through the plants differently. For example, nitrogen is very mobile and will move throughout the plant’s tissues– from old leaves to newly formed foliage.

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With a nitrogen deficiency, the oldest leaves are first affected, while the scarce nutrient moves to the newer ones.

The opposite happens with less mobile nutrients like calcium. The newer foliage is affected by calcium deficiency first because the old leaves use the limited nutrient before the younger ones get a chance.

You can tell what nutrients your plants lack from where the yellowing begins.

You can also differentiate between the yellowing caused by nutrient deficiencies and the one caused by other factors. When the veins in the leaves remain green, but the tissues surrounding them have turned yellow, it is usually a sign of nutrient deficiencies.

Here’s a quick way to know which nutrient is lacking in your plants, so you know what to correct:


Nitrogen

Yellowing in entire leaves beginning from the oldest ones before spreading to new foliage.

Potassium

Black spots over leaves.
Older leaves are affected first, and the margins appear yellow and burnt.

Phosphorus

Brown spots on leaves, especially at the tips.
May also cause a reddish-purple or an unnatural dark green color.
Affects older leaves first, which wither.

Calcium

● Causes younger leaves to turn yellow or light-green between veins.
● Leaves develop brown or black tips.
Causes rot at the blossoming end of fruits and vegetables.

Iron

Yellowing between veins of younger leaves.
In severe cases, it may bleach the whole leaf white.

Magnesium

Yellow patches form between the veins that remain green.
Affects older leaves first.

Sulfur

Uniform yellowing of the entire leaves.
Begins with young leaves first.

Copper, Zinc, Manganese

Causes yellowing between veins on younger leaves.

Boron

Yellow edges on younger leaves.
Death of leaf edges and terminal buds.

How to Correct Nutrient Deficiencies In Your Tank?

Fertilizers are a great way to improve the amount and quality of nutrients in your tank. You can use liquid or powdered fertilizers to make it easier for your plants to absorb them.

Some notable fertilizers that work well with aquarium plants are:

Seachem flourish
Easy root tabs/ Easy green
API leaf zone

2. Overfertilization

yellowing-due-to-overfertilization

While it’s a good idea to use fertilizers to improve the concentration of vital nutrients in your tank, overfertilization can have profound implications.

Adding too much fertilizer results in toxicity. This toxicity burns the leaves and gives them a yellow appearance.

How To Prevent Overfertilization?

Make sure the nutrients remain in the optimal range to avoid overfertilization. The right concentrations of the nutrients in your tank are

Nitrogen 10-25 mg/l
Phosphorus 0.1-1.5 mg/l
Potassium 10-30 mg/l
Iron 0.1-0.5 mg/l
Magnesium 5-10 mg/l

While this should work for most of the common aquarium plants, feel free to make any modifications according to the plant types you are growing.

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3. Inadequate Light

Tank-lighting

Inadequate exposure to light is probably one of the most notable reasons for your plant’s discoloration.

Like terrestrial plants, aquarium plants also require exposure to sufficient light to grow. They harness light to drive biological processes like photosynthesis.

Without light, chlorophyll is not produced sufficiently, resulting in leaves becoming yellow.

How to Manage Lighting In Your Aquarium?

Aquarium plants need full exposure to light for about 10-12 hours daily. You should place the plants somewhere they can receive sunlight or use artificial lighting.

Some suitable light sources include high-output fluorescent or LED strips that can provide 4-5 watts of light per gallon of tank.

4. Diseases

Diseases-in-aquarium-plants

Some plant diseases caused by viruses, bacteria, and fungi can cause yellowing in leaves. One way to tell what pathogen is responsible is to check the pattern of yellowing and other accompanying symptoms.

  • Fungal diseases may cause chlorosis (the yellowing of the leaves) and leaf spots, among other symptoms.
  • A bacterial infection will cause the leaves to develop brown leaf spots with a yellow halo surrounding them.
  • A viral infection will cause the leaves to turn yellow and form a mosaic pattern.

How to Control Diseases?

These pathogens can get into your tank due to poor aquarium hygiene. Be proactive in combating the pathogen, or it will destroy the plants and ravish your entire tank in no time.

Maintain good tank hygiene at all times and remove all the affected leaves before the disease spreads.

Sometimes, these pathogens are spread by disease-carrying pests. Ensure your tank is free from pests and insects by using appropriate pesticides or insecticides to control their population.

5. Poor Substrate

If you use the wrong substrate for your aquarium plants, it will affect the supply of required nutrients. When plants don’t have access to the nutrients needed to grow, they become deficient and change color (as described above).

How To Choose The Right Substrate For Your Aquarium Plants?

Research your chosen aquarium plants thoroughly so you can find a suitable substrate to use. Some plants can grow well without soil, while others require supplemental aid to grow well.

The best substrate for aquatic plants is fine to medium or coarse-sized gravel. For optimum results, you can mix both types of textures. However, avoid using very fine sand as a substrate to prevent compactness.

6. Choosing Wrong Plants For Your Tank

Leaves-floating-on-water

Plants require specific environments to grow well. You can’t just randomly pick any plant and put them in your aquarium. 

Some aquatic plants like to be completely submerged under water, while others prefer staying above the water level.

Likewise, some do not like confined spaces while others do.

Choose your plants carefully and ensure you create the right environment for them to grow, or they’ll begin to deteriorate and change color.

7. Aging

Aging-in-plants

Sometimes, the yellowing of your plants could be due to the natural aging process. Older plants have a higher risk of deterioration because they slowly lose the ability to absorb nutrients.

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If your plants are yellowing due to age, there’s not much you can do to reverse or help the situation.

8. Carbon Dioxide (CO2) Deficiency

Aquarium plants need carbon dioxide to grow. In its absence, several damages could occur, including stunted growth and yellowing of leaves.

The optimum concentration of CO2 in the tank should be between 15-30 mg/l. Anything outside those figures could mean trouble for your plants.

How To Manage CO2 Deficiency?

Introduce carbon dioxide supplements to increase its concentration in your tank. You can also use CO2 injection systems in the form of liquid CO2 or pressurized carbon dioxide gas.

However, remember to turn off the injection systems at night (when the plants themselves produce CO2) to prevent oversaturation.

9. Water Quality

The quality of water in the tank can affect the overall plant health. Poor water quality can cause the leaves to turn yellow and deteriorate.

Some factors contributing to poor water quality include water hardness, temperature, pH, and more.

Plants need optimal water temperature to perform biological functions. Leaves will turn yellow in low temperatures. If the cold persists for a long time, the yellow leaves could deteriorate and turn brown.
Plants need optimum water pH to remain green. Outside the recommended pH range, the leaves begin turning yellow.

How To Improve Water Quality?

Ensure that the pH in your tank is between 6.5-7 and the water hardness remains between 50-100 ppm.
Adjust the water temperature to suit the needs of your plants.
  • The optimal temperature range for most aquarium plants is between 74-80°F. Make sure to keep the temperature at this level.  
  • If your aquarium heater is faulty, fix or change it.

10. Poor Tank Hygiene

Contaminated-tank-water

Poor tank hygiene could cause the water in the tank to become contaminated. It exposes the plants to diseases that affect their ability to absorb nutrients.

Organic waste such as fish or snail poop and other impurities are the biggest culprits. The result is the plants turning yellow.

How To Prevent Water Contamination?

To prevent contamination in the tank, check the tank filter to see if it is clogged and clean it. Make sure you do not lose the nitrifying bacteria that live on the filter media.

Clean your tank regularly and change the water to reduce the accumulation of impurities and the risk of contamination.

You can also consider adding bio media or beneficial live bacteria to your tank to improve the water quality. These bacteria also prevent algal growth.

Final Words

There are several reasons why your aquarium plants could be turning yellow. Luckily, most of them are reversible and easy to control, especially if spotted early.

Regular maintenance and care go a long way in ensuring your aquarium plants are healthy.

Aquarium Plants Turning Yellow: 10 Reasons And Solutions

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