Why Are My Aquarium Plants Turning Yellow? And What To Do About It.

Why Are My Aquarium Plants Turning Yellow?

In this article, we’ll answer the question of why are your aquarium plants turning yellow, tell you why it’s happening, and show you how to prevent it from happening any more.

Overall, the plants in your fish tank can turn yellow or turn brown when the factors critical to their survival are unavailable or compromised.

One of the signs that your aquarium is no longer healthy – or getting there – is the yellowing of their leaves. And there are several reasons behind this, which we will discuss below.


A Few Plant Care Essentials

Why Are My Plants Dying?

One of the first reasons your plant could start turning yellow is lack of light.

Aquatic Plants require light for photosynthesis, which is how they manufacture their food. If they don’t get enough light, they slowly turn yellow and eventually die away.

Another reason living plants in aquarium turn yellow is when they’re not getting enough nutrients to promote their growth.

Three of the most common aquarium plant deficiency that would cause new leaves to turn yellow are:

  • Nitrogen Deficiency
  • Iron Deficiency
  • Potassium Deficiency
  • Phosphate Deficiency

However, there are a few other deficiencies that can impact the growth of our aquatic plants.

Other Nutrient Deficiency That Can Affect Your Plants Growth

  • Magnesium Deficiency
  • Calcium Deficiency

How to Fix A Nutrient Deficiency And Stop Your Plants From Turning Yellow

The solution to yellow plants is pretty simple; you need to ensure that a sufficient amount of nutrients that your plant needs are readily available in the water. That said, there are also a few other items below that you should take into consideration.

Water Quality

Different plants have different water requirements, but for most aquatic plants, you’ll want to keep a pH of 6.5 and 7 and general hardness between 50 ppm and 100 ppm. To control algae growth on the leaves, nitrates should also be under 10ppm and phosphates below 0.5ppm.

As for temperature, you should keep it from 74° to 80° F. The water must be changed regularly – 10% every week or 25% twice a week. Bio media will do well for your filter as it can eliminate organic wastes that cloud up the water and keep light from penetrating.

Another useful technique is reverse osmosis or just use deionized water if your tap water is unhealthy for aquatic plants.

Overall, proper circulation is vital to plant health. It prevents algae growth and the accumulation of organic waste on leaves and ensures that plants always get all the nutrients they need.


How much light your planted aquarium needs depends on which plants you want to have and the height of your tank. Some species need more light to survive, and since light does not usually pass through water enough, you need to install a stronger light source for a taller tank.

Generally, aquatic plants thrive in full-spectrum light with a color temperature of 6,500K and 8,000K. Be sure to pick a light source that is made particularly for plants, such as LED and high-output T5 fluorescent.

Aquatic plants are known to thrive with about 10 to 12 hours of lighting daily. Take note, though, that keeping the light on for longer will not make up for weak lighting. Also, make sure to follow a constant day/night pattern. If your tank has no built-in timer, use any digital timer, you have to make sure the light is consistently on schedule.

For best light output, get a new high-output T5 or another fluorescent bulb ever year. And don’t forget to clean the glass covers so that the light can entirely pass through into the water.


In most cases, our best options are fine to medium gravel or coarse wand, but you can combine this with various grades to achieve the texture and aesthetics you want.

Stay away from the extremes though, such as super-fine sand, which is too compact and lacks breathability, and super-coarse gravel, which tends to collect too much organic waste and is too loose for plant anchoring.

You can set up a 2 to 3-inch” base and slope it upward toward the back of the tank. For more depth and dimension, add some hills and valleys too. Be sure to keep carbonate-based substrates (dolomite, crushed oyster, etc.) as these can increase the water’s alkalinity to dangerous levels.

Food For Aquarium Plants = Nutrients

Plants that go inside your tank are not the same as those you’ll find outside, and one of the ways they differ is in the nutrients each group needs. Aquatic plants need nitrogen, phosphorous & potassium, or NPK and plenty of minerals like magnesium, iron.

Some nitrogen and phosphorous needs can come from fish waste and uneaten food, but you’ll have to add the micro-minerals yourself regularly.

Another thing to keep in mind is that plants can absorb these nutrients through their roots, leaves, or both, depending on the species. For those that take in nutrients from the roots, you can mix in laterite (a type of clay-rich in iron) , or you can also use other types of substrates that already have nutrients packed into them.

. Make sure you use tabs for aquatic plants, though and not those for houseplants, which have different formulas that may not be beneficial inside a tank.

Carbon Dioxide

Carbon is an essential thing that helps you grow healthy plants.

Aquatic plants, in particular, can take up CO2 in the day and go through the opposite process during night time. A lot of plant aficionados use supplemental CO2 at daytime to improve plant color, size, and growth rate. You can add carbon using liquid or tablet supplements or even homemade yeast generators.

All of these methods work, but a pressurized injection system synced with aquarium lighting can have dramatic results. Because CO2 pumps up plant growth, you need to raise the dose for your liquid nutrients to stay in step.

Choosing the Right Aquatic Plants

For someone who wants to solve the problem of yellowing, the answer is simply to choose the right plants from the start. Spend some time researching the types of plants that are best for your fish tank. Better yet, talk to an expert and ask for advice.

Understand what your plant needs for nutrients and give it to them!

In general, remember that tall or fast-growing plants should be placed at the back, while low-profile plants can be placed in front. For broadleaf plants, you’ll want to position them somewhere in the middle.

A lot of foreground species grow sideways, so be sure to have adequate lateral space to accommodate them.

And avoid putting shorter plants next to broadleaf species, which are taller and can thus prevent the light from penetrating to the back.

How Do I Keep My Plants Green?

While every plant and aquarium is different, in my own experience, I’ve found consistency is critical. Many plants will adapt to the environment they are placed in.

If you add nutrients each day, continue to do that. Don’t add aquarium plant fertilizers one day and not the next. This can confuse your plants, and they will start to use the nutrients in their system to feed, slowly killing them. When this happens, they aren’t using the nutrients in the water, which can lead to algae.

If you run your lights, put them on a timer, and keep it on schedule. If you find it’s too much or too little, slowly adjust to accommodate.

Lastly, experiment, have fun, and hopefully, your plants won’t turn yellow.

Why Are My Aquarium Plants Turning Yellow And What To Do About It.

Jack Dempsey
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