Black spots on aquarium plants are a worrying content if you see your plants looking differently and less fresh like they used to.

Black Spots on Aquarium Plants

However, knowing what exactly causes those black spots will help you treat your aquarium better. Now, let’s see what will be the most likely cause of your aquarium plants turning black.

What Are the Causes of Black Spots on Your Aquarium Plants?

The causes of black spots on your aquarium plants would be due to excess nitrate, phosphate issues, an insufficient amount of light, the presence of beard algae, or lastly temperature issues in the tank. These reasons would harm your plant and cause them to develop dark dots.

All it takes is a step back and a close-up inspection, especially when you’re an aquarist; then, caring for the fish is only just a single task on the long list of duties you need to tend to. Don’t worry, your aquatic plants won’t be as demanding as the fish, but they still can develop some concerning signs. The most obvious and deadly of which is going to be the darkening of leaves.

– Excess Nitrate

When you see that your plants are starting to look different, discolored, and developing black spots, you would worry. Note that nitrate is one of the primary food sources for your aquatic plants, and they need it for survival. However, there can always be too much of a good thing and the same goes with nitrogen, but the result of the excess will be harming.

Too much of this substance will prevent iron synthesis in the plant and cause iron deficiency in plant cells. This is how leaves all turn their colors, but it ain’t going to be soon before your leaves go black, and it will often be the end of your aquarium plant. In short, nitrate toxicity is a hard thing to treat, although this is a reversible factor, showing you that the plant is not at great risk.

– Phosphate Issues

Too much phosphate will usually happen when there’s too much-decaying plant and fish matter floating around in your water. Phosphates do get eaten, filtered, or otherwise expelled from the tank, but if you have some left then this is an alarming issue. In other words, your water filter should be kept working in perfect condition, so always check up on it and remove and wipe any decay from the aquarium glass, or else the plants will be damaged and weakened.

– Insufficient Lighting

Light is a necessary ingredient in plant life; however, excess aquarium lighting can cause a damaging effect. It can cause your live plants to overuse the gases in their habitat which can lead to all kinds of problems and their ability to perform photosynthesis, and it’s this problem that causes leaves to go black, which would first start with little circular patches.

Causes of Black Spots on Plants in Aquarium

While we are at light matters, low light exposure can be a problem too. What happens is that algae forming on the walls of your aquarium can block out the sunlight from reaching your plants and cause them to go black.

– Black Beard Algae

The black beard algae are quite a pest in your watery environment. These black algae will spread fast and make any surface unsightly. They’re known to latch onto the very plants too, and they would develop quite strongly on them.

Like your normal algae, these will block out the sun and light from reaching your plants. Other than that they are completely harmless, so a lot of people often overlook them before they become an issue.

Black algae will also fight for the nutrients with other plants and this is what can make your plants turn black as well. Always look to keep your fish tank clean and don’t allow these to form.

– Temperature Issues

Outside conditions will matter just as much as the inside ones will. Most tanks require water temperature to be at 85 degrees Fahrenheit on average, while the cooler end of the scale is more appreciated than the upper. Sometimes we forget to check our water temperature and aid in the problem creation, and that stresses the plants and results in a change of their normal state.

Especially when our freshwater aquariums are fish-free for prolonged periods. As a result, your fish tank will become largely plant-life-based, and as such temperatures will often rise and these can prove deadly for your plants. Eventually, if kept in this condition, your plants will turn brown and black as a result.

How To Tackle the Black Spots on Aquarium Plants?

To tackle the black spots on aquarium plants you should try to manage the phosphate level in the tank, and also increase the CO2 content as well. You could also add algae-eating fish, and lastly, try to clean the tank with chemicals.

– Phosphate Management

Phosphates are highly toxic compounds for all life in your aquarium, not just your plants. You should remove any decayed matter from the tank as you possibly can. After this, you should change at least 25 percent of your entire water volume with a fresh supply and recheck your phosphate levels. If the damage wasn’t huge enough to start with, your plants should spur back to life pretty soon as the level is now better.

– Increase CO2 Content

Your CO2 levels are important for the life inside the tank. CO2 levels shouldn’t sit too low, as your plants may begin to die. In this case, you must always manage and restock the carbon dioxide in the tank. Plants will produce CO2 on their own, but if the situation even goes slightly stale they will fail to do so, so it’s important to recharge.

CO2 injections are one possible method to help you deal with low levels of this compound. With this method, you won’t even have to wait long for the CO2 levels to get back to normal. You may also try to use a pressurized container to pump this gas into the water through a narrow valve. However, using this method can be expensive, and you may resort to a CO2 supplement of sorts.

Moreover, these will be available at much cheaper prices and get the job done quickly too. You should choose the one that perfectly matches your tank situation, and the info can usually be found on the label.

Tackle the Black Spots on Aquarium Plants

In this case, you can always try to work out different home remedies as well. For instance, you can mix some yeast and sugar, because these are two ingredients that can release CO2 when mixed with water. Yeast can be a good start for beginners not already managing big tanks, and to tackle the spots away.

– Add Algae Eating Fish

As mentioned, black beard algae are your true enemies, they will harm the life and the exterior of the aquarium plant. How they start is by having the strength to pop out of their own accord and in any situation, but dealing with them can become quite a nuisance, at times, which is an issue that deepens on the intensity of their growth.

The best way to fight and prevent black beard algae is when the infestation is still in the early stages. You can try to acquire algae-eating fish to help you out. Some of the most popular algae-eating fish species will include American flag fish, Black molly fish, Flying fox, and Rosy barbs.

Fish won’t be able to consume the mature algae formed from these pests, but they won’t even have to as they will eat the algae while still young, which means when the latter is harming the plant already. In this case, they will try to eat it, but of course, the algae are dense already, which will give you a very slow result, because they may keep on growing.

– Cleaning the Tank Using Chemicals

Hydrogen peroxide is an effective alga combatant too, and this method includes removing all of the affected plants and elements from the tank. What you can do is simply wipe the hydrogen peroxide solution on them. If your algae issue is already too far gone, then you should consider wiping your entire tank clean with this compound.

You can always choose to remove the algae by hand, but this method isn’t as effective and can leave algae cells to begin spreading anew. The black beard algae aren’t such a severe enemy, or at least they often don’t get to be as most aquarium enthusiasts tackle them early on, but when you clean the tank thoroughly you can remove them with the right chemicals.

What you should do is ensure a well and scheduled maintenance routine that will involve a thorough tank cleaning and regular water changes. This will help you stabilize the environment even before anything bad can happen. Remember to always try to keep your tank clean and well-lit to prevent the algae from forming from the decayed plant matter.

Black Spots on Freshwater Aquarium Plants


Those black spots on your freshwater aquarium greenies aren’t a pretty sight by no means. These can sometimes lead to serious issues, so let’s remind ourselves:

  • Always do a close inspection and try to guess where the issues come from, and you can try to clean it deeply so that all will be fixed.
  • Your tank life will always appreciate a quick CO2 boost and management of the nitrate too.
  • What you should always aim for is maintaining a perfect tank balance by regular cleaning, keeping the setup well-lit, and taking care of your CO2 levels.

Now that you know why your water plants will go black, it’s time to up your aquarium game!

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