Aquarium Plant Nutrient Deficiency – Everything You Need to Know

Disclosure: I may earn a commission when you purchase through my affiliate links. As an Amazon Associate I earn from qualifying purchases. – read more

So, you have the perfect tank set-up. The water is pristine and all the parameters are within range. You picked the perfect soil and you’re diligent about fertilizing. But somehow, your plants look off and you get very little growth. What’s up with that?

There’s likely a nutrient deficiency at play here. Besides poor water parameters, nutrient deficiencies are the second most common cause of stunted growth, leaf defects, and death of aquatic plants. And yes, these deficiencies can still appear even if you use fertilizers.

If this sounds like your situation, keep reading! I’ll teach you everything you need to know to spot, understand, and treat nutrient deficiencies in aquarium plants.

Nutrient Deficiency Chart in Aquarium Plants

Like all other living organisms, plants need a variety of micronutrients to sustain growth and just to stay healthy in general. Nutrient deficiencies have a negative impact and can affect the appearance of the plant. If left untreated for too long, they can even kill your plants altogether.

Obviously, you’ll want to do something to solve the problem asap. But first, you must be able to identify the cause. If your aquarium plants aren’t thriving and you don’t know why this chart should come in handy.

I’ve included some of the most common symptoms and the most likely deficiency that causes them. This should help you figure out the root of the problem:

Symptom Possible Deficiency
Old leaves appear yellow and withered Nitrogen
Old leaves appear yellow with dark patches Phosphate
Old leaves turning yellow or pale, veins are dark Magnesium
Old leaves darken and have a brownish underside Phosphate
New leaves turning yellow or pale, veins are dark Iron
New leaves appear twisted and misshapen Calcium, Phosphate
Leaves developing a reddish hue Nitrogen
Pale leaf veins; leaves wilt and drop Copper
Dark spots on leaves Potassium, Iron
Leaves develop small holes with discolored margins Potassium, Manganese, Iron
Leaves develop discolored, translucent tips Nitrogen
Leaves develop yellowing at the tips and edges Potassium
Leaf edges appear discolored and curl inward Potassium
Stunted growth in new leaves Boron, Calcium, Nitrogen, Iron, Potassium
Slow-growing stems Phosphate, Nitrogen
Leaf buds droop and appear discolored Boron

Overall, the symptoms and the underlying cause are pretty straightforward. But notice there’s sometimes an overlap between different deficiencies. Sometimes, you might also get similar symptoms in both old and new leaves.

The distinction is very important, as the underlying cause can be completely different. For example, pale old leaves signify a magnesium deficiency, while pale new leaves can hint toward an iron deficiency. For an accurate diagnosis, you should pay close attention to how your plants develop, when the symptoms appear, and how they manifest.

6 Common Nutrient Deficiencies in Aquarium Plants

There are many trace nutrients in the soil and water. Plants need a combination of everything to stay healthy. But some nutrient deficiencies are more common than others. So, to keep things short, I’m going to go over some of the most important nutrient deficiencies you’re likely to encounter in aquarium plants.

– Nitrogen Deficiency (N)

Nitrogen is a colorless, odorless gas and one of the most common elements in the world. You might have already read about it before setting up your tank. “Nitrogen cycle” is a common phrase in the aquarium hobby. As you might guess by now, nitrogen is closely connected to the level of nitrates and ammonia in the aquarium.

The problem with nitrogen is that you need to keep a tight balance. Without enough waste in the aquarium, the nitrifying bacteria won’t convert enough nitrogen for the plants. But you need to perform regular water changes to keep your fish healthy. Large and frequent water changes reduce the concentration of nitrates and nitrogen in the water.

This is good for your fish, but a no-no for your plants. Nitrogen is vital for the well-functioning of aquarium plants. This element is one of the most important components of chlorophyll. Without it, the plants lose their rich green pigmentation. And without enough chlorophyll, plants can’t convert light into energy. It’s a vicious cycle.

In the case of nitrogen deficiency, the leaves might become yellow, discolored, or reddish, depending on the plant species. Older leaves begin to wither away, while younger leaves stop growing or grow at a slower rate than normal.

The optimal nitrogen concentration for plants is 5-30 milligrams per liter. The easiest way to increase the nitrogen concentration in the water is by using liquid fertilizers. More on this later.

– Calcium Deficiency (Ca)

Calcium is an important mineral for the structure and strength of plant cell walls. Without enough calcium in the water, the plant’s cell walls can’t form properly. Think of the plant’s cells as your skeleton. Low calcium in humans leads to rickets, a softening of the bones. This leads to crooked limbs, especially the legs and the spine.

Something similar happens in plants. The fibrous walls that give the plant its shape and structure become weaker. This leads to stunted growth and misshapen leaves. The leaves might appear asymmetrical, curly, and maybe even slightly crinkled.

Calcium deficiency usually occurs in soft water aquariums. There’s a direct correlation between the water hardness level and the calcium concentration. Remember, calcium is a mineral. The more minerals in the water, the higher the hardness level and vice-versa.

If you’re using filtered water for your aquarium, remember to test the hardness level. You might have to add some calcium via a fortified substrate or crushed coral. The optimal calcium concentration for healthy plant growth is 20-30 milligrams per liter.

– Iron Deficiency (Fe)

Iron is an important metal the plants need to maintain color and proper function. Without enough iron, newly sprouted leaves will appear pale green or even white. Similar to nitrogen, iron is crucial for the creation of chlorophyll. Iron also supports plant metabolism in other ways. It’s used in the formation of several other pigments and enzymes.

Not enough iron means not enough chlorophyll and pigments. This means the plant loses its color and ability to metabolize other nutrients. What’s worth noting is that iron deficiency mostly affects the young leaves. Older leaves maintain their original color.

In the case of severe iron deficiency, the leaves will begin developing dark spots and holes. This means the leaves are actively dying. Overall, optimal iron levels for aquarium plants fall between 0.05-0.1 milligrams per liter. Large and quick-growing plants require more.

– Phosphate Deficiency (PO4)

Phosphate is crucial for the creation of adenosine triphosphate (ATP). ATP is a molecule that helps all living organisms use energy to sustain bodily functions. In plants, this includes photosynthesis and growth. So, it makes sense that phosphate deficiency leads to stunted growth and loss of pigmentation.

This deficiency sets in and worsens very rapidly because plants consume phosphate in high concentrations. The first sign of deficiency is a darkening of the leaves. As the deficiency progresses, the leaves turn yellow and develop brown splotches. Soon after, the leaves will die and either fall off or start growing algae.

The symptoms affect older leaves first. You might notice stunted growth or a deformed shape in newly-sprouted leaves. The optimal concentration of phosphate to maintain healthy plants is 0.1-1.5 milligrams per liter.

Sometimes, the levels drop below this range because of certain filter media. Phosphate-absorbing pads are a common culprit. These are often advertised as a solution to algae infestation. The problem is that most aquarium plants also need plenty of phosphate to thrive.

– Magnesium Deficiency (Mg)

Magnesium is another metal with an important role in plant photosynthesis. Like iron, this metal is a crucial part of the plant’s chlorophyll. Without enough magnesium, plants can’t sustain their green pigmentation or metabolize nutrients. Unsurprisingly, magnesium deficiency leads to loss of color in the leaves.

When magnesium deficiency sets in the leaves turn pale or yellow but the veins remain dark. This deficiency manifests similarly to a lack of iron. But while iron deficiency affects new leaves, magnesium deficiency appears in the older leaves. With magnesium deficiency, the leaf edges might also droop.

Plants need lots of magnesium to stay healthy, over 10 milligrams per liter. That’s a huge quantity, but most fertilizers contain this mineral. As such, magnesium deficiency is rarer than iron deficiency. Sometimes, a magnesium deficiency might arise due to a nutrient imbalance.

Magnesium deficiency is often connected to calcium. These two minerals compete to be absorbed by aquarium plants. Too much of either mineral will deplete the other. So, if the plant is getting too much calcium, this can lead to a magnesium deficiency. The ideal balance for optimal nutrient uptake is 4:1-2:1. The total concentration of calcium should be no higher than four times the total magnesium.

– Potassium Deficiency (K)

Potassium is a metal that plants need for the transportation and storage of water, nutrients, and sugars. Without enough potassium, the other goodies that plants need won’t go where they’re supposed to. Potassium also helps with root strength and vitality.

Potassium deficiency manifests in many ways, mimicking multiple other deficiencies. The main telltale sign is the appearance of small dark spots on the leaves, mainly around the edges and towards the tips. As the deficiency progresses, these spots widen and transform into holes. The hole margins appear dark or discolored.

Sometimes, the affected leaves might turn yellow before dying off. New leaves will show stunted growth. There’s a lot of symptom overlap between iron, magnesium, and potassium, as you can see. The optimal potassium concentration for healthy plant growth is 5-10 milligrams per liter. Some potassium-hungry plants, like Java Fern and Anubias, might require closer to 15 milligrams per liter.

How to Add Nutrients to Your Aquarium?

In theory, treating a nutrient deficiency is pretty simple. You just need to replenish the missing nutrients in your aquarium. But how do you do that? Well, there are a few different ways. The method you choose will depend on the missing nutrients you’re trying to replace, as well as your preferences. The most common methods include:

Fertilizer

Fertilizer is a quick and easy fix for a variety of nutrient deficiencies. It’s like a multi-vitamin pill for plants. Fertilizer works best for fixing a variety of deficiencies, especially nitrogen. Most fertilizers contain nutrients like nitrogen, phosphorus, iron, manganese, magnesium, potassium, copper, boron, nickel, chlorine, cobalt, and molybdenum.

But you’ll have to check the product label. Some fertilizers contain a little bit of everything, others contain just two or three nutrients for targeted care. A good fertilizer will also state the concentration for each nutrient.

Remember that as your plants grow, you’ll have to increase the fertilizer dose. Larger plants require more nutrients. What was once enough, might no longer suffice. The beauty of fertilizer is that you have many options available, including liquid fertilizer, root tabs, and fortified, pre-packed substrates.

Liquid fertilizer should be dosed regularly. This is a fast-release nutrient bomb so it’s perfect if you need to replenish nutrients quickly. Root tabs and substrates are slow-release sources. They need less frequent replacements, but it’s harder to calculate the proper dose.

Nutrient-specific supplements

Some deficiencies are stubborn and difficult to fix with just fertilizer. If you need a large dose and high precision, I recommend looking into nutrient-specific supplements. Such supplements are the best option for fixing iron, potassium, phosphate, and magnesium deficiencies. You can also find supplements for other nutrients.

Targeted nutrient supplements are also desirable to mega-dosing on fertilizer. Too much fertilizer might encourage algae growth. The high concentrations of certain nutrients might also affect the fish and other critters in the aquarium.

The great thing about supplements is that they’re accessible and easy to use. They typically come in liquid form and you can purchase various sizes, depending on the product. Measuring and dosing are pretty straightforward. These supplements come in bottles with either pumps or measuring caps.

Epsom salt

If you have some epsom salt lying around, you can also use that to increase nutrient levels. Epsom salt, also known as magnesium sulfate, contains, well, magnesium. So, this trusty infection treatment that your fish love is also good for plants. If your plants have a magnesium deficiency, that is.

A few caveats though— Epsom salt is difficult to dose, compared to other targeted supplements. It’s easy to overdo it. Too much epsom salt will increase the water hardness. This can, in turn, affect your fish and also the plants. Be careful!

Crushed Coral

Crushed coral contains a combination of minerals including calcium, magnesium, and small concentrations of selenium and chromium. The most abundant component of coral is calcium carbonate. You can use this to increase the calcium concentrations in the water.

Crushed coral is basically a slow-release calcium supplement. The fact that it comes together with magnesium is also great. Remember, you need to keep a tight balance between these two minerals! Plus, adding some crushed coral on top of your substrate will also enhance the appearance of your aquarium.

Keep in mind that using crushed coral isn’t as precise as a targeted liquid supplement. The extra calcium and magnesium in this substrate will also affect water hardness levels. You could get some sudden fluctuation in parameters when adding the crushed coral to the aquarium. This can be a problem if you have fish in the tank.

What Else do Aquarium Plants Need?

So far, we’ve covered nitrogen and a variety of minerals. These are all very important for the health and vitality of your plants. But that’s just half of the story. Sometimes, your plants might be suffering for other reasons.

If you’re using the best fertilizers and supplements, and your plants are still stunted and discolored, something else must be going on. Most probably, it’s one of these factors:

– Light

Light is crucial for all plants, aquatic species included. Without light, plants will starve to death, despite all the nutrients you pump into the tank. That’s the extreme scenario. In your case, your plants are getting some light, but it’s not enough to sustain growth. If your plants appear otherwise healthy but they won’t grow, this is probably the reason.

Remember, plants use light to complete the photosynthesis process. They convert light into sugars. These sugars provide the energy that plants need to grow and sustain themselves. You wouldn’t thrive with just vitamins and no calories (aka food), and neither do plants.

If you have a tall aquarium, you might want to crank up the light a little bit. The lighting might be too weak to reach the plants at the bottom of the tank. Similarly, if you have very tall plants that cover the water surface, you’ll need to trim them. These plants take up space and shade the other plants at the bottom of the tank.

– Oxygen

Plants are beneficial because they produce oxygen. But did you know plants must also breathe oxygen? It sounds bizarre, but it’s true! Plants must take in oxygen to perform a process called “aerobic respiration”. Through this process, plants break down the sugars they produce. Then, these sugars are released to travel freely where they’re needed for nourishment.

Oxygen usually runs low in the aquarium for two reasons. First, you have no surface agitation. The water is completely still. This makes the exchange of gases more difficult, so not enough oxygen returns to the tank. An easy fix would be adding an air stone to the aquarium. Air stones create bubbles that break the surface tension. This results in better oxygen exchange.

Secondly, you might have floating or tall-growing plants that cover the aquarium surface. These plants act as a barrier between the water and the outside of the tank. Even if you use an air stone, such plants can prevent the gas exchange between the water and the air. Trimming at least some of the plants to create open spots at the surface should help.

– CO2

All plants require CO2 for photosynthesis. Without enough CO2, plants can’t create adequate amounts of “food” to thrive. This is perhaps the most important nutrient because plants consume it constantly and in large quantities. Low CO2 will present similarly to many other nutrient deficiencies we’ve discussed previously.

Signs of low CO2 include yellowing or pale leaves, stunted growth, algae infestation, and sudden plant death. If you have a densely-planted aquarium the CO2 produced by the fish might not be enough. In this case, CO2 fertilization becomes necessary.

You can fertilize your plants with either liquid CO2 or with a CO2 injection system. The preferred concentration for healthy plant growth would be 15-30 milligrams per liter. If your aquarium has lots of foliage and large-growing plants, stick to the higher end of this range. You can monitor the CO2 concentration using a drop checker.

Conclusion

Sometimes, you do everything right and your plants are still withering away. The cause is often a sneaky nutrient deficiency. The most commonly deficient nutrients in aquarium plants are iron, magnesium, calcium, potassium, phosphate, and nitrogen.

It’s hard to determine exactly what deficiency you’re dealing with. But there are some telltale signs to help you narrow the list down. The table I’ve included in this article covers most of the common symptoms and the associated deficiencies.

If you think a deficiency might be causing all this, there are multiple ways to fix this issue. A balanced, general-use fertilizer contains most nutrients in suitable concentrations. You can also use nutrient-specific supplements for a targeted cure. Besides nutrients, you should also consider the light exposure and the oxygen and CO2 concentrations in your aquarium. 

avatar I’m Fabian, aquarium fish breeder and founder of this website. I’ve been keeping fish, since I was a kid. On this blog, I share a lot of information about the aquarium hobby and various fish species that I like. Please leave a comment if you have any question.

Related Articles

Leave a Comment

Your email address will not be published.