Why Your Aquarium Plants are Turning Brown

Why Your Aquarium Plants are Turning Brown

AquariaWise is a participant in the Amazon Associates program and a few other affiliate programs and may earn from qualifying purchases at no extra cost to you. However, we have vetted every program in this guide and believe they are the best for generating affiliate revenue. You can read our full affiliate disclosure in our privacy notice.

Aquarium plants assuredly spruce your fish tank and provide a refuge for your skittish and shy fishies. They also act as perfect breeding grounds for many species of tropical fish.

However, you want them to remain green and alive, which is sadly not always the case. Live aquatic plants (like any other species) tend to turn color if there is a deficiency or excess of nutrients in their environment, in this case, your aquarium water.

From experience, most aquarium plants turn brown and die when there are excess (or insufficient) phosphates or nitrates in the water column, though, in lesser occasions, a brown-tinge may appear on leaves and stems due to a lack of potassium (together with holes on leaves).

Poor water conditions might also be the reason, same as algae growing on your plants. This is particularly apparent in tanks with too much light exposure and nutrients.

Brown algae (diatoms) might be the reason for brown plants, more so in newer fish tanks. They mostly appear in the aquarium before the nitrogen cycle gets up and running when the nutrients balance is off.

Aquarium plants need a few nutrients to be well balanced for them to grow beautifully. This will also help prevent problems like brown or black leaves. These crucial elements include potassium, phosphorus, and nitrogen.

Below is a detailed breakdown of all possible reasons why your aquarium plants might be turning brown.

Aquarium Plants Turning Brown or Black

The main reason why aquarium plants change color is because of an imbalance in the light or nutrients required for them to thrive. Most often, the plants suffer from deficiencies, more so when new, but an oversupply of these two elements might cause damage to your plants as well.

Sadly, many fish keepers focus on deficiencies and forget too much is not ideal. For this reason, I recommend you concentrate on balancing the nutrients as opposed to increasing them haphazardly.

With that said, aquatic plants require several nutrients, though they vary in the amount needed. Essentially, they’ll use up more nitrogen, phosphorus, and potassium, and lesser amounts of iron, magnesium, boron, carbon, and others.

Most nitrogen and phosphates come from fish waste, leftover food, and other organic debris. An excess or deficiency of which may result in a color change in your plants that includes brown shades.

See below instance that may cause your live aquarium plants to take on a brown hue.

Nitrogen for Aquarium Plants

As I mentioned, macronutrients (nitrogen, phosphorus, potassium) are crucial elements required by plants to thrive; aquatic species included. Nitrogen is expressly vital, and luckily, is readily available in aquarium environments.

Nitrogen can be absorbed by aquarium plants in various forms, including ammonium, urea, and nitrates, meaning live plants are also quite useful in fish tanks with excess nitrates.

Nitrogen deficiency in aquarium plants leads to yellowing of leaves, which if left unresolved, will cause the foliage to turn brown, black, and die, starting from with the older leaves.

Younger foliages will appear weakly and have crippled growth, and in some plant species, you may even notice the leaves take on a purple hue.

To ensure your plants have sufficient amount of nitrogen, (assuming the amounts from your fish waste are not enough) dose your tank with liquid fertilizers that are rich in nitrogen, such as Flourish Nitrogen.

Phosphorous for Aquarium Plants

Phosporous deficiency in aquatic plants can easily be seen as fast-growing stems and slow development of shot tips. Most plants also turn dark and take on a violet hue.

That said, if your live aquarium plants start to turn brown or black and die, it might be a sign of excess phosphate levels in your tank, though it could also be excess nitrates.

To bring the levels down and maintain the desired balance of both phosphates and nitrates in the water column, do one large-water change, then continue with regular replacements to ensure the levels don’t come back up.

In planted fish tanks, phosphates concentrations of about 0.1 to 1 ppm (mg/L) are recommended, though the optimum is 0.5ppm. To know the amounts in your water, you can do a standard water test that is readily available commercially.

Potassium for Aquarium Plants

Typically, the lack of potassium in aquarium plants lead to perforated leaves due to dying tissues, though in the beginning, the only recognizable sign is small black dots that eventually grow into holes, partially outlined in yellow or black.

Though the dots are black, they at times take a lighter hue that might be mistaken for a brown color. Either way, if not resolved, the deficiency will kill your plants gradually.

So to keep your plants alive and healthy, use liquid fertilizer to dose your already existing plants, and roots tabs when introducing new plantlets in the substrate.

My top choice would be seachem flourish when looking to use an all-around fertilizer. Flourish tabs are best if looking to start new plant in a substrate.

Aquarium Plants Turning Brown and Transparent

Sometimes, your plants will turn brown and transparent, which is mainly caused by an iron deficiency, sometimes coupled with low potassium, phosphorus, or nitrogen levels.

Essentially, a lack of iron should only result in transparent leaves, though it’s also not uncommon for dying leaves to get a yellow, then a brown tinge even with enough of other nutrients.

In case of iron deficiency, you should supplement your plants with a fertilizer rich in iron such as flourish iron.

Brown Aquarium Plants Due To Algae

One other reason that might be causing your aquarium plants to turn brown would be algae. Normal green algae is less likely to have such an effect, but diatoms are notoriously culprit to browning of not just plants, but most fish tank surfaces and decorations.

Diatoms (generally referred to as brown algae in the hobby) are a type of “algae” that mostly develops in newer fish tanks.

Availability of nutrients, including phosphorous, nitrates, and silicates, plus sufficient light help brown algae to thrive.

These algae form soft, slimy, clumpy patches on surfaces, and mostly appears when cycling and maturing a new fish tank. Luckily, the problem quite often resolves itself within a few months.

In case it develops on plants in a mature tank, the most likely culprit would be silicates seeing that they are diatoms favorite food source. They find it delicious and will thrive in an aquarium that has high amounts.

In the abscense of silicate, brown algae can also survive on nitrates and phosphates, both of which are readily available in a tank with a lot of uncleaned fish waste and leftover food.

Therfore, if your diatom problem does not resolve itself, consider removing excess waster, and use remedies like manually removing the algae from affected areas.

Vacuuming your sand substrate, (sand substrates are more likely to help diatoms thrive because of excess silicates), cleaning your aquarium plants, and scraping your glass will also go a long way in solving your brown alge problem.

That’s all, happy 🦐🐠 fish keeping.

Eddie Waithaka

Resident Content Creator and Marketer at AquariaWise who talks about aquariums and fish and aquascapes a lot.

Author image

AquariaWise Newsletter

Get exclusive the tips, that we only share with our subscribers. Enter your email address below.

Your subscription could not be saved. Please try again.
Your subscription has been successful.

This site uses cookies. By continuing to browse the site, you are agreeing to our use of cookies. Okay, thanks