6 Common Signs Of Too Much Light On Aquarium Plants

Caring for aquarium plants is not an easy task. Many people make the mistake of providing them with excessive lighting and experience a terrible problem.

So, what are the signs of too much light on aquarium plants? Let’s join us and try to listen to your plants. Then, you will know what they need.

Signs Of Too Much Light On Aquarium Plants

You can observe your aquatic plants and fish’s behaviors to determine if there is too much light for the plants. The six most apparent signs include:

Overgrown plants

Seeing the aquatic plant’s rapid expansion seems delightful at first. However, once you stop observing, the expansion speed has become too fast, and things turn out problematic.

Because of the frequent pruning needed for overgrown plants, your maintenance burden will increase significantly. This issue becomes much more vital if you only have a small aquarium.

Furthermore, since plants take up space, your fish can’t move freely. They could get nervous and display symptoms like aggressiveness and appetite loss.

Color changing

When the leaves of aquatic plants change color, they may receive excessive lighting.

For example, if they live in a dark place and you move it to a better-lit one, they will turn yellow.

Your plants need one week to get back to their normal hue. Be aware that it will only happen if you alter the illumination to meet its requirements.

If the leaves become red or purple, the light is too strong. As a result, chlorophyll will break down, resulting in color change.

And if the leaves start to turn brown, it may be due to excessive heat caused by extreme brightness.

aquarium plant's color changing

The leaf color will change

Brown edges on the leaves

Plants with brown edges on their leaves are under heat stress from intense illumination.

Rotting leaves

Rotting leaves usually result from algae development, not light issues.

However, since improper illumination can lead to algae covering the plants excessively, we still include rotting leaves in this section.

Your plants can become overwhelmed by uncontrolled algae blooms caused by excessive sun exposure. The leaves might then begin to rot as a consequence.

Stressed fish

Your plants may not instantly display symptoms of too much lighting, but it doesn’t mean they aren’t in danger.

Watching your fish is one of the simplest ways to see if there is too much light since they will show signs of discomfort, such as:

  • Aggression
  • Appetite loss
  • Diseases, like ich
  • Terrible scale quality
  • Weight issues

Algae covering plants

An overabundance of nutrients and light will cause uncontrollable algae formation.

Many fish owners think that moving their tanks to a darker place can solve this problem, but it doesn’t work that way.

To avoid nutrient accumulation in your aquarium, limit the amount of light it gets, changes the water frequently, and avoid overfeeding.

algae covering plants

Algae expansion is not a good sign

How Much Light Should Aquatic Plants Get?

Aquatic plants are available in numerous varieties, each with particular requirements. As a result, there is no broadly applicable guideline for how much illumination they need.

Often, these plants need eight to ten hours of lighting every day. Their best light sources are LED light, fluorescent light, and indirect sunlight.

The light color is also important. It would be best to give aquatic plants a lighting mix of green, blue, and red lamps.

Consider the number of aquatic plants in the tank and the lighting settings. For example, your tank might not need extra lighting in a space with sufficient light.

​Here is our recommendation for setting up the light for your live plants based on their characteristics:

Type of plant Intensity of light
Easy plants 11-20 lumens per liter
Medium plants 21-40 lumens per liter
Advanced plants > 40 lumens per liter

Extra Aquarium Lighting Tips

Aquatic plants need moist conditions to not die. Hence, avoid putting them in running water since the chlorine may cause damage or even death to your plants.

You may sometimes notice a white slime on the leaves, but don’t worry. They are beneficial bacteria that your fish can eat. The slime also plays a vital role in keeping your tank in homeostasis.

Besides, make sure that the plants hold the substrate firmly. Avoid planting them in big bushes because they need space to grow and receive sufficient light on all of their leaves.

Many aquatic plants have natural growth mechanisms. Species like Vallisneria have runners that break through the substrate and grow close to the parent plant. You can remove the runners and plant them again to create a new scrub.

Click this video to learn more about aquarium lighting in a planted tank:


set up the light appropriately

Try to set up the light appropriately

Frequently Asked Questions

1. Can a fish tank light be too bright?

No. The lighting should not be too harsh for a regular aquarium as it may stress your fish. Excessive light can also cause algae development.

2. Do fish like color-changing lights?

There won’t be any problems if you simply change one regular aquarium bulb with another bulb. Fish may adapt to various hues.

However, it’s preferable to avoid changing their coloration too often. Otherwise, the lighting will stress your pets.

3. Do fish prefer white or blue light?

Although fish can see well under both colors, blue light is more advantageous since it stimulates coral growth.

4. Can I leave my aquarium light on 24/7?

No. Keeping the light all the time will encourage algae growth.

And cleaning the algae from the tank might take weeks or even months. Aside from that, fish need darkness to rest and sleep as humans do.

5. Do LED lights hurt fish eyes?

Unlike your underwater vegetation, fish are less dependent on light. Therefore, LEDs won’t have an impact on their eyes.


Lighting is essential for your live plants’ growth, significantly affecting your fish’s health. So try to set it properly, and the plants will appreciate your effort.

Do you have any problems when caring for your fish tank? Feel free to ask if you need any further information. Thank you for reading!