Why Are Aquarium Plants Turning Yellow?

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Plants are pretty much vital to any aquatic environment, especially a closed one like an aquarium. They are relatively easy to maintain since caring for the fish means also caring for the plants. That being said, you should consider your plant’s needs since they often require special favors.

Today, we will discuss what happens when the plants begin to change their color and turn yellow. Why? Because plants only change their coloring when dying. So, your tank plants turning yellow should put you on high alert.

That’s because whatever’s affecting your plants will most definitely affect the entire environment, along with any aquatic creatures it may be housing.

7 Reasons Aquarium Plants are Turning Yellow

While plants will experience various color intensities depending on the quantity of light and nutrients, they will never turn yellow, brown, or black if they’re healthy. If your plant begins to turn yellow, something’s wrong with it.

There are 7 primary causes for plants turning yellow:

– Nutrient Deficiency

Plants require a variety of nutrients to remain healthy, grow properly, and exhibit their strongest coloring. Any nutrient deficiency will impact the plant differently, interfering with its physiology and altering its colors.

Unfortunately, you have quite a few nutrients to worry about, and they’re not exactly easy to measure in the water. On the other hand, there are ways to identify the type of deficiency by assessing your plant’s looks. In this sense, you have:

  • Potassium deficiency – This nutrient plays a vital role in the plant’s physiological processes. The plant will use potassium to form sugars, aid in protein synthesis, and grow stronger and more well-developed roots. This nutrient is also key in strengthening the plant’s immune response to various diseases. If your plants experience potassium deficiency, expect the older leaves to turn yellow on the edges, with the inner area remaining fairly green. As the leaf dies, the edges will turn rusty-brown and curl in some cases.
  • Nitrogen deficiency – Nitrogen is another key component in the plant’s internal processes. It is used to boost plant growth, allowing the plant to reach maturity faster. In case of nitrogen deficiency, the plant will display hindered growth and generalized yellowing. Older leaves will become yellow first, then turn brown and fall off.
  • Phosphorus deficiency – Plants use phosphorus to perform photosynthesis, synthesize protein, and stimulate blooming and germination. Phosphorus deficiency will generally create trademark symptoms, consisting of yellow, brown, or bronze spots in the underside of the leaves. The plants will also display hindered growth and will remain smaller than healthier ones.
  • Magnesium deficiency – This is an interesting one since magnesium plays a variety of critical roles in the plant’s physiological functioning. Magnesium is necessary for plants to produce sugars and fats and aid in the general absorption of other nutrients. Also, magnesium deficiency manifests via loss of chlorophyll, causing the leaves to look drained of color. Most leaves will turn pale yellow and will begin to fall of in more advanced stages.

We could mention other nutrient deficiencies here, like iron, boron, manganese, zinc, and calcium, each coming with several symptoms and effects along the way. The idea is to provide the plant with a nutritious environment to prevent deficiencies and boost its growth and healthy long-term. I recommend mineralizing the water properly to prevent any deficiencies that could kill your plants.

– Poor Water Quality

There are 2 aspects to discuss here:

Dirty Water

If the tank water is too dirty, it will hold less nutrients and will pack more ammonia and nitrites, which are deadly in high-enough concentrations. These chemicals become a severe problem in unclean tanks with little-to-no maintenance. Fish waste, dead organic matter, and food residues will increase ammonia levels fast and foul the environment.

Fish will experience the effects first since they are far more sensitive to ammonia and other harmful chemicals than the plants. This is why it’s imperative to keep the tank clean and have a robust maintenance routine in place.

Improper Water Parameters

This issue also falls under the ‘poor water quality’ descriptor. Different plants require different water parameters in terms of temperature, lighting, pH, and hardness. Improper water conditions will affect the plants accordingly, causing loss of color, loss of leaves, and even death.

Fortunately, this is an easy fix, you only need to assess the water conditions regularly and, most importantly, understand what your plants need.

You can easily fix all dirty water problems by maintaining an adequate maintenance routine. You should immediately assess all major water parameters if your plants exhibit signs of discoloration or generalized discomfort. They can be saved if you take adequate measures fast.

– Light Intensity

Proper lighting is crucial for plants since it supports their physiological functioning. Sunlight supports photosynthesis and eases nutrient assimilation, allowing plants to grow faster, larger, and remain healthier and more colorful in the long run. Aquarium plants should get around 6-8 hours of lighting every day.

However, this isn’t the only thing that matters. Light intensity is also a make-or-break deal. Too much is just as dangerous as too little but for different reasons. Not enough lighting will hinder the plant’s ability to extract and process nutrients and perform photosynthesis. This will effectively kill the plant quite fast.

If there’s excessive light, the plant will consume too much CO2 from its environment, depleting the CO2 reserves. This will also impact its ability to perform photosynthesis. Not to mention, excessive lighting is also linked to algae bloom, which will create an entire array of problems.

If your plant exhibits discoloration or dying leaves, assess the oxygen levels in the tank. As a general rule, if your plants display pearling (bubbles visible on the leaves), that’s a sign that the water oxygenation is high.

– Wrong Substrate

This point is naturally relevant to rooted plants that will take their nutrients from the substrate. The type of substrate to use makes a massive difference in this sense. Soil is the most obvious choice since it anchors the plant better than any other option. It’s also the plant’s natural substrate, providing a variety of nutrients that are not available in other substrates.

Avoid gravel and rocks for obvious reasons since these won’t keep the plants rooted. Sand isn’t that much of a better option either. Sand is typically too compact and lacks the nutrient content that plants need.

There’s also another problem to consider. Fish tanks require a different approach than plant-only setups. You should also consider what your fish need in terms of the substrate. If you have bottom-dwellers, you should have sand as the substrate of choice, but this isn’t ideal for rooted plants. Figure out a balance between fish and plants in terms of substrate, and you should be good.

– Lack of CO2

This is a common problem in most aquariums. Especially those not getting proper maintenance and care in the long run. Plants consume plenty of CO2 during the day to support their photosynthesis and produce oxygen as a byproduct. CO2 deficiency is deadly in the long run.

The plant will exhibit discoloration, stunted growth and will begin to lose leaves if the situation isn’t rectified fast. So, you absolutely need a CO2 testing kit to make sure everything remains within the desired parameters.

– Compacted or Damaged Roots

This is a uniquely difficult problem to assess because the roots are hidden in the substrate. There are 2 different aspects to discuss here:

  • Damaged roots – A lot of things can damage the plants’ roots in a tank. Fish rank among the most common causes. Cichlids, for instance, are notorious substrate diggers that can damage the plants’ roots in the process. The damages are usually invisible since the substrate hides them, but you will soon notice the effects. Since it experiences damaged roots, the plant will no longer be able to extract nutrients from the substrate as efficiently. So, it will exhibit signs of nutrient deficiency and begin to die off soon.
  • Compacted roots – Substrate compaction is a well-researched topic that refers to the soil being overly compressed. This makes the soil denser with less space between the particles, which will put a lot of stress on the plants’ roots. The roots won’t be able to grow and extract nutrients normally anymore due to the excessive mechanical stress. This problem tends to occur in tanks with sandy substrate.

Unfortunately, it may be tricky to assess root problems due to them being buried and out of sight. That being said, there are signs to watch out for, including the plant presenting discoloration and nutrient deficiencies. If everything else is normal, including water nutrient presence, CO2, lighting, oxygenation, and overall water quality, the roots might be the problem.

– Natural Aging

This might sound obvious, but we had to mention it here since it fools a lot of aquarists, including the more experienced ones. It can sometimes be difficult to assess a plant’s age when buying it. This can lead to confusion when the plant begins to lose its coloring and leaves several months later, or even sooner.

If there’s no obvious reason for the plant’s unexpected and unwanted transformation, you may have to accept the ‘getting old’ answer. Aging plants can no longer extract nutrients properly, so they will begin to die off gradually. This process may take time, so you can either remove them completely or cut the yellowing leaves and keep the plant a bit longer.

Eventually, you will need to remove it to prevent the dead organic matter from altering the water’s chemistry.

How to Keep Aquarium Plants Green and Healthy?

Keeping plants in good condition is key to preserving their health in the long run. It’s also worth mentioning that caring for the plants ultimately means caring for the environment as a whole. So, there are several ways by which you can improve your plants’ health:

  • Monitor CO2 levels – The CO2 is key here since it can render all other parameters useless. It doesn’t matter how clean and stable the environment is if there isn’t enough CO2 for your plants. They will begin to die. To prevent that, always have a tester kit nearby, ready to use in case plants display signs of CO2 deprivation. An injector kit is also necessary to replenish the CO2 levels and correct the problem before advancing any further.
  • Ensure proper tank maintenance – Having a solid maintenance routine in place is key to preventing a variety of problems. I recommend removing any excess waste that may alter the water’s chemistry life, fish poop, food leftovers, and any other organic matter than may decay and release ammonia. Water changes are also necessary to keep the environment fresh and well oxygenated.
  • Prevent nutrient deficiencies – Nutrient deficiencies are more frequent than you might think, especially due to improper water changes. Everybody knows, by this point, not to use tap water when performing a water change. Tap water can contain chlorine and chloramines, which are poison to fish and plants. RO/DI water types are more reliable since they’ve been sterilized. The problem is that the sterilization process also strips away all of the nutrients, depriving the plants and fish of the minerals and vitamins they need to thrive. To prevent this problem, you should also use a water conditioner to re-mineralize it before performing your water change routine.
  • Prevent overstocking – Overstocking plants can lead to major problems fast. One of them is the competition over CO2, soon leading to scarcity and CO2 deprivation. The other is the competition over nutrients with similarly obvious results. Only keep as many plants as necessary, based on the tank’s size and overall layout.
  • Prevent algaeBlack Beard algae are killers when ignored and taken lightly. They will spread throughout the entire tank, cover the plants, and limit or eliminate their access to sunlight. To keep the algae in check, consider having a few algae eaters around, reducing the light’s intensity, keeping the tank clean, and keeping the nitrate levels low. These measures should inhibit algae development consistently.

Aside from these measures, you should also choose an adequate substrate for rooted plants to help them thrive in the long run.


Plants will change color for a variety of reasons. The sooner you identify those reasons, the easier it will be to prevent further damage and save your plants. Fortunately, this article has provided you with plenty of insight into the most common causes and solutions that relate to yellowing plants.

Adopt these measures to your situation, and your plants will thrive.

Author Image Fabian
I’m Fabian, aquarium fish breeder and founder of this website. I’ve been keeping fish, since I was a kid. On this blog, I share a lot of information about the aquarium hobby and various fish species that I like. Please leave a comment if you have any question.
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