7 Reasons Your Aquarium Plants Are Turning Yellow (& What To Do)

The last time you checked, your aquarium plants floated like a tropical green jungle among the fish at the bottom of your fish tank. Now, they are starting to turn yellow and die. Many people encounter this problem when their aquatic plants start to take on a sickly hue. Instead of throwing your plants out and starting over, there are several important ways to identify and fix the problem.

If your aquarium plants turn yellow, it’s usually something that you can fix. For example, most aquarium plants turn yellow due to lack of sunlight or fertilizer, water temperature, the wrong pH, nutrition deficiencies, tank maintenance issues, or disease.

Discover the top 7 reasons why aquarium plants turn yellow and how to solve the problem.

Why Are My Aquarium Plants Turning Yellow?

1. Water Temperature

If your aquarium plants are turning yellow, the water in the tank might be too cold. Since green leaves will turn yellow if the water stays cold for a long time, it’s a good idea to check the temperature of your tank. It’s best to keep the water at 74° to 80° F to avoid plants turning yellow.

2. Disease

If you typically keep your aquarium at optimal temperatures, it’s time to check to see if a disease is causing your plants to turn a yellow color. Microbes are a common reason why aquatic plants lose their natural color and turn yellow.

Yellowing leaves are often an initial sign that disease is present in the tank. If a microbial disease isn’t caught and resolved, the whole plant can die.  

To avoid an overgrowth of bacteria and fungi in your tank, which could harm both plants and fish, maintain good basic tank hygiene. Most tanks need cleaning every two weeks to ensure proper cleanliness.

3. Lack of Fertilizer

A third reason that your plants can turn yellow is a nutritional deficiency. If your plants aren’t getting the fertilizer that they need, they won’t have the ability to grow and fight off disease. If your plants keep turning yellow, there’s a good chance that they need fertilizer. These can include a liquid fertilizer, base fertilizer, or root fertilizer depending on the type of plant.  

Underwater plants in the Rio Negro, Brazil.

4. Lack of Light 

Like most plants, aquarium plants need enough light to keep them from dying. Although they might live among rocks and fish at the bottom of a tank, aquatic plants require a minimum of 10-12 hours of light to thrive.

Aquatic plants need to do photosynthesis each day. When marine plants aren’t exposed to an intense light source for enough time, they can’t complete photosynthesis that generates food from light and carbon dioxide to create chlorophyll and oxygen as a byproduct.  

If your tank doesn’t have access to a sufficient sunlight source, you will need to install a full-spectrum fluorescent light or LED REB light to help your plants flourish. Make sure that they receive at least 6-8 hours of sunlight or strong artificial light for a chunk of time every day.

5. Nitrogen, Potassium, Iron, or Magnesium Deficiency

If your aquatic plants are turning yellow, it’s time to get scientific with their nutrient list. If a plant doesn’t receive specific nutrients such as potassium, magnesium, iron, or nitrogen, it can’t create chlorophyll which keeps leaves green.

Check your plants’ foliage. If a potassium deficiency is causing the leaves to turn yellow, the yellow tinge will occur towards the edge or tip of the leaves. Magnesium deficiency can also be a culprit if the leaves turn yellow while the veins on the leaf stay green.

Aquatic plants need and intake nitrogen in several ways that include ammonia, nitrate, and urea.

You can identify a lack of nitrogen by checking the older leaves on the bottom. If they turned a translucent yellow, then it’s time to add some nitrogen to your water column. The final nutritional reason that can cause plants to yellow is an iron deficiency. With a lack of iron, the leaves will fade out to a pale-yellow hue.

6. pH Levels

Another reason that can cause aquatic plants to turn yellow is if there are the wrong pH levels in the tank’s water.

For example, most aquariums require a pH that lies between 6.5 and 7.8. Make sure that the general hardness is 50 ppm – 100 ppm and that the alkaline levels fall between 54 ppm and 140 ppm (3° and 8° dKH). Keep nitrates below 10 ppm, while phosphates need to fall below 0.5 pp to prevent algae growth and yellowed leaves.

7. Old Plants

If you’ve tried everything on this list and your plants don’t respond to treatment or turn yellow again, it’s possible that your plants are turning yellow due to the aging process.

Since older plants can’t keep consuming nutrition, they will eventually degrade and die. If that’s the case, you won’t be able to change or stop this process and will just need to replace your plants when they die.

How to Avoid Aquarium Plants Turning Yellow

1.    Choose the Right Plants

To keep your plants from turning yellow, it’s important to choose the proper plants in the first place. Take time to research the kinds of plants that will flourish in your aquarium. You can even reach out to an aquatic plant expert for more advice.

For example, if you want to have some tall plants or species that grow faster, put these at the back of your tank. Put shorter plants in front so that they aren’t blocked by bigger plants.

If you have broadleaf plants, arrange these in the center of the tank. If you have foreground types, they can expand sideways, so it’s best to make sure that your tank is big enough to allow for lateral growth.

Finally, don’t put short plants right next to broadleaf plants. These species create taller foliage that can prevent light from getting all the way to the back of the tank. Careful selection and arrangement can help you maximize your light source and avoid yellow plants that are overcrowded or don’t receive enough light.

2.    Check pH and Clean the Tank

As discussed, you will want to check the pH levels and maintain a clean tank by cleaning it every two weeks. You will also need to change the water often. This means that you will want to change up to 25% of the water twice a week. Use bio media for a filter since this reduces organic waste that causes cloudy water and prevents light from penetrating into the tank. Try reverse osmosis or deionized water to keep your plants green and healthy.

3.    Fertilize

Ensure that your aquatic plants have the nutrients that they need by adding fertilizer that is rich in nitrogen, potassium, phosphorous, iron, and magnesium minerals. If you have the kind of plants that consume nutrients via their root system, you can add a kind of clay-rich iron called laterite or another type of substrate. Make sure that you get a formula that is specifically created for aquatic plants rather than houseplants.

Although fish and food bits do add some nitrogen and phosphorous, you’ll want to regularly pour these micro-minerals into the water to keep your plants happy.

4.    Don’t Fertilize Too Much

Moderation is key here. Although fertilizers can help your plants grow and keep them green, too much of a good thing can turn toxic.

If you add too many nutrients to an aquarium too fast, it can create a chemical reaction that scorches the foliage and turns leaves yellow.

5.    The Carbon Factor

This one’s easy to miss when you’re looking for ways to keep your plants from turning yellow. Carbon is a vital part of growing healthy aquarium plants. These underwater plants absorb CO2 during the day, then reverse that process at night. Some plant experts add extra CO2 during the day to help plants grow faster and maintain their foliage color.

You can add carbon to the tank with a tablet or liquid supplements. Another option is to make your own yeast generator at home. One of the best ways to add carbon to your plants’ diet is to install an injection system that works with pressure and tank lighting to boost growth and health results.

6.    Let There Be Light

Keep in mind that your aquarium plants will vary depending on the type of plants used and the size of your tank. If you have a taller tank that is filled with plants, make sure that the light source that you install is stronger.

In general, aquatic plants need full-spectrum light. The color temperature should be from 6,500K – 8,000K. You can use a plant-specific light source such as an LED or T5 fluorescent with a high output. Using a timer can help keep a consistent and natural pattern that mimics daytime and nighttime.  

7.    Be Consistent

As with everything, consistency is essential. If you add fertilizer every day, keep doing it. Don’t add nutrients one day, and then forget about it the next day. Inconsistency can confuse aquatic plants and make them consume nutrients from their own system rather than depend on an erratic feeding schedule.

Keep lights running on a schedule. Make any changes slowly and keep it consistent. Over time, your plants will adapt and thrive in a consistently healthy environment. It may take some time for damaged or yellow leaves to regain their color. Experiment, and hopefully, your plants will soon return to normal.

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Recap

If your aquatic plants are turning yellow, it’s usually an easy fix with some time and effort. It may take a little detective work to determine if your tank pH is off or if your plants need some nutritional support.

Like most living things, marine plants need light to survive, so flip the switch, open the curtains, or move the tank to a location where your plants can receive light. Maintaining a clean tank will not only make your aquatic world sparkle, but it will reduce bacterial diseases that can cause plants to turn yellow.

The good news is that it is entirely possible to stop your aquatic plants from turning yellow and create a healthy underwater place for your fish to thrive.