Why Are My Aquarium Plants Turning Brown? (5 Common Reasons)

If you’ve ever tried growing live plants before eventually you’ll run into the problem of brown leaves, brown stems, or even dead plants! Why do our aquarium plants turn brown? 

This is a sign that there’s an underlying issue we need to address. So let’s inquire into the main reasons why aquarium plants turn brown!

Potential Reasons Why Your Aquarium Plants Are Turning Brown

Here are a few of the most common reasons why your aquarium plants are turning brown:

Not Enough Light

Of all the reasons we have to deal with brown aquarium plants low light levels are probably the most common reason. Plants of all kinds need some light to survive. 

Many low light plants like Java Fern and Anubias can get by with the dimmest of aquarium hoods. But most plants will eventually wither without proper lighting.

Plants usually start by dropping their lowest leaves that are furthest from the light. They then take on a stringy appearance, focusing all of their growth into new leaves near the growing tip as they race for the surface. If you see this pattern arising it’s clear your lights aren’t strong enough.

It’s also important that you provide the right spectrum for your plants. Light intensity is just one part of the issue. You also need to provide PAR (photosynthetically active radiation). Which can be understood simply as the wavelengths of light that plants actually use for photosynthesis. 

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For example, it does no good to provide freshwater plants with marine high-intensity actinic lighting; it’s the wrong spectrum.

Instead, you should look at full-spectrum fluorescent and LED fixtures. Especially LED lights; modern fixtures are not only very reasonably priced but low energy and long lasting as well.

What kind of plant you’re growing also affects the light intensity they need. Even a good quality full-spectrum light may still cause low-growing carpeting aquarium plants to wither anyway if they are too far to make good use of the output!

Nutrient Deficiencies

Nutrient deficiencies are probably the second most common reason why aquarium plants turn brown. Even if your lighting is strong, plants need certain elements and chemicals to survive, just like animals.

Fish can provide quite a bit of these essential elements through their waste but not all of them. A good aquarium plant substrate is not only enriched with essential elements but can bind to free floating molecules to hold them in place until the plants uptake them through their roots!

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Nitrogen

Nitrogen, in the form of ammonia, is the element animals are best at providing to plants. And so long as your tank is properly cycled, your plants can also consume nitrite and nitrate as bacteria break down ammonia.

However if you have a deficiency due to low stocking levels or loads of plants, the older leaves will begin to fade. This color change typically starts from the tips of the leaves. First they turn light green, then yellow, and eventually they turn brown as they decay.

Nitrogen is used in the production of chlorophyll and protein and all plants require a regular supply of it. Nearly all aquarium plant fertilizers include Nitrogen. However a booster shot of just Nitrogen is helpful if it’s the only element your plants are missing!

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Phosphorus

When plants are lacking phosphorus the leaves turn yellow in their entirety with large brown patches. These patches are where germs have begun to decay the leaf structure, causing it to rot away. Once this process begins algae can also grow in as the plant can no longer fend off invasions.

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Phosphorus is used by plants and animals to make ATP (adenosine triphosphate), an essential molecule for energy consumption. It can be found in animal waste and leftover food. However if your plants are low it can be easily added with chemical fertilizers!

Potassium

Potassium deficiency is fortunately one of the easiest problems to diagnose. Large holes begin to develop centrally within the leaves with yellow-brown rims. Over time the leaves turn yellow and then brown as they begin to die.

Potassium is an essential element used by plants to regulate the flow of water, sugar, and nutrients throughout their systems.

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Like the other major elements Potassium can be easily supplemented with liquid fertilizers like Seachem Flourish Potassium!

Brown Algae

Look very carefully at your plant leaves. Are your aquarium plants really turning brown or are they covered with a dusty, rust-like coating of brown? It’s possible you may be dealing with a brown algae infestation!

The more familiar green algae is caused by microscopic single celled organisms and cyanobacteria. Brown algae, on the other hand, is caused by organisms called diatoms. 

Technically they aren’t plants but a type of phytoplankton that are actually very useful! Diatoms are estimated to generate between 20-50% of the oxygen we breathe!

However in the aquarium they are less useful because they coat every surface in a rusty brown slime. While they aren’t strictly harmful, they look terrible and they do reduce the amount of light your plants take in. There are also very few algae eaters that eat brown algae. 

Instead, you’ll need to try physical or chemical means of removing them. I cover how to deal with brown algae in greater detail here!

Animals Eating Your Plants

Herbivores are another reason why your plants may be turning brown. Do you have fish like Cyprinids (Barbs, Danios, Goldfish), Silver Dollars, Mollies, and other known vegetarians? 

These fish love picking at soft plants like Cabomba and Anacharis; these plants are like having a floating salad bar at the ready. While it’s good nutrition for your fish the plants can only take so much grazing before they begin to suffer. 

Silver Dollars have big crunching teeth that let them eat not only leaves but they can mow stems right to the ground. Even tough, bitter plants like Anubias and African Water Fern will eventually be eaten by them!

Freshwater snails are somewhat tricky. Most actually don’t eat fresh plants if given the choice. They much prefer slightly decayed, dead leaves, leftover food, and other detritus. However if they have nothing else to eat they may turn to fresh greens, especially large Apple and Rabbit Snails. 

So if you start to see your snails mowing down leaves simply provide them with sinking pellets or blanched vegetables like Spinach or Zucchini. These vegetables are softer, already dead, and will attract all of your snails to the table!

Plant Needs to Establish Itself

Believe it or not plants can experience stress! Most plants really hate to be moved; once they root somewhere they don’t like being shifted around. If you have Goldfish or Cichlids that like to dig and pluck them from the substrate…Or you as an aquarist keep moving them around trying to find the perfect arrangement for your planted tank

They may start to brown and wither as they shift internal resources towards survival. Cryptocorynes are especially infamous for this. They not only turn brown but the leaves actually dissolve within just a few days. 

Usually they will only lose a ew leaves but sometimes the entire upper portion of the plant browns and dies! Fortunately, it will eventually recover and grow new leaves.

So be careful with sudden shifts in water parameters or moving your plants around frequently. Plants want to remain undisturbed and thrive in stable conditions!

Conclusion

Unfortunately, there are many possible reasons why your aquarium plants are turning brown. Fortunately, they are mostly very easy to fix! 

Whether it’s lack of light, nutrients, algae issues, predators, or shifts in parameters…Plants are very resilient organisms and will quickly bounce back once you solve the mystery!

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