Fertilizers for aquarium plants

Aquatic plants will grow healthy and adequately only if they receive sufficient amounts of light, water and necessary nutrients. These last are provided to them as aquarium plant fertilizers. There are many ways to do it. In the aquarium trade, there are available liquid fertilizers that we add into the water column, root tabs or dry fertilizers designed to be amended into the soil and released to the aquatic plants over time. The source of essential trace elements is also pre-packed substrates. Using plant fertilizers guarantees high yields.

The demand for aquarium plant fertilizers can differ depending on water parameters, the intensity of lighting in the aquarium, and carbon. Freshwater plants grow at varying rates. Well-lit water plants need more aquarium fertilizers, and those with limited access to light will become slow-growing plants and use less of them. In the case of a poorly lit aquarium, you have to be careful not to overdo it because the excessive aquarium plant fertilizer can lead to algae bloom.

Always dose the

Essential nutrients in aquarium plant fertilizers

Aquatic plants consist of chemical compounds from several elements. We divide them into two groups: macronutrients and micro ones.

At first sight, it may sound confusing, but it is straightforward. This division exists to tell the difference between those elements whose consumption is relatively high and those elements which are not that commonly used by plants. It does not mean that any of these is less or more important. If some of these are lacking, most plants will not grow healthy or not grow at all.


In a nutshell, macronutrients are used by plants in large amounts. These elements are labelled as NPK, which means successively:

Nitrogen (N)

This element is crucial because it primarily builds proteins and plant hormones. This one is used by plants for leaf and stem growth. It is also an essential part of chlorophyll.

Nitrogen deficiency usually is shown by the fact that old leaves turn a yellowish colour and are reabsorbed from the end to the stem over time. Usually, the first symptoms are visible on older, lower-set leaves. Still, prolonged-lasting nitrogen deficiency can also impact newer ones, and the growth tips may twist strangely- you would see that immediately.

In a heavily stocked tank, there will probably be no need to do any nitrogen supplementation. The endless nitrogen cycle will deliver this element in the form of nitrates, and adding more nitrogen can destroy the stability of the well-cycled aquarium water.

Phosphorous (P)

Live plants need it to flower or fruit, but it is also crucial for any process in which plants use energy. It takes part in transporting and storing up the energy inside cells.

Phosphate deficiency can cause dead patches on leaves, which may fall off quickly- similar to nitrogen deficiency in the early stages. It also stops plant growth.

On the other hand, adding too much phosphorous may result in an algae bloom.

Potassium (K)

Aquatic plants need potassium sulfate to strengthen plant roots and leaves. It is often used in the form of potassium sulfate, providing both potassium and sulfur.

Potassium deficiency can be visible as pin-holes on leaves. If your planted tank has too much potassium, it may block the process of absorbing the essential micronutrients.

Except for the most popular NPK elements, we may also specify other macronutrients like i.g.:

Calcium (Ca) and Magnesium (Mg) are responsible for water hardness. They are usually found in tap water, so you do not have to supplement them. But if the water is too soft, calcium and magnesium are definitely needed as a fertilizer.

Sulfur (S)- is quite interesting because it is crucial while plants do photosynthesis. Lacking sulfur is visible in new leaves. Their colour is light and looks withered.

Macro elements in planted tanks can be compared to carbohydrates and proteins that we eat in our food. Most aquarium hobbyists believe that aquarium plant fertilizers with macro elements should be applied regularly an hour before they turn on the lights in the aquarium.


Briefly speaking, microelements are used in a planted tank in small quantities for specific functions. We may point out some of them:

Iron (Fe)

Iron is often said to be one of the most essential of all trace elements. Plants use iron to produce chlorophyll- a green pigment that helps plants absorb light and make energy. In general, fast-growing plants that need bright lighting use lots of energy. To get more energy, they often require supplemental iron to produce chlorophyll.

Without iron, plants cannot produce chlorophyll, which gives plants oxygen and healthy green colour. The newer leaves will grow in pale light green or white with strange spotting, while older leaves will appear normal. The veins of the new leaf growth will remain dark compared to the discoloured leaves.


Some of you may be confused, but it is worth mentioning that this element is also classified as a microelement necessary to our planted aquarium. Well, as you already know, microelements are used in tiny quantities and in tap water, there is chlorine. And sometimes there is too much of it, which is the problem. You must remember that the excess chlorine is toxic and can negatively affect plant growth and other functions. It is not likely that in the freshwater tanks, you will still use aquarium plant fertilizer with much chlorine in it.

If you are going to change the water and you know that there are vast amounts of chlorine, try to prepare it for at least 12 hours before adding it. During this time, the chlorine will evaporate. You should use a tap water conditioner if there are also chemical compounds like chloramine.

There are also many other trace elements that many plants use, for example:

Boron (B)

Manganese (Mn)

Zinc (Zn)

Copper (Cu)

Cobalt (Co)

Nickel (Ni)

All of these vital micronutrients are used to keep plant health at a high level. Compared to our food, they would be vitamins and minerals of the planted tank. Contrary to all the nutrients mentioned in the macro section, most hobbyists say that micro fertilizer should be applied when the light is switched off.

How to choose the best aquarium plant fertilizers?

The best aquarium plant fertilizer should be plainly labelled with the listed presence of particular elements and how much of each is present. If such information is lacking, you may look for other fertilizers. You can provide veterinary advice or ask at the local pet store if unsure. The same thing happens to us when we buy food in supermarkets. People want to know what is inside their product.

Which form of plant fertilizer to choose?

As was mentioned at the beginning, aquarium fertilizers are available in different forms. Try to understand what you buy because they are not all the same.

Liquid fertilizer

First, liquid fertilizers are fertilizers dissolved in water that you pour into the tank. As with all things, this solution- all in one fertilizer- has its pros and cons.

The advantages are clear:

You don't need to measure out individual nutrients of your plant fertilizer.

Just follow simple instructions.

Reasonable value. One bottle of liquid fertilizer is enough for many gallons.

When it comes to the disadvantages, you have to know:

Probably you do not need the wide range of nutrients involved in aquarium plant fertilizer, and there is nothing you can do to separate them.

The aquarium water can become dirty after using this liquid fertilizer. Fortunately, it clears up after a few hours.

Pre-packed substrates

Secondly, pre-packed substrates are a popular choice. This aquarium plant fertilizer has nutrients, and your aquarium plants can source them from the roots. And this is the exact reason why this is not always the best aquarium plant fertilizer. They are suitable for plants with roots, such as Sword plants or Cryptocoryne. But if you plan on buying rootless or floating aquatic plants, this solution is not for you.

Aquarium plant fertilizer root tabs

The third option is root tabs that are nothing more than a compressed aquarium fertilizer. They are designed to use if you have an inert substrate like sand or gravel.

This aquarium plant fertilizer is an excellent choice for those who want cost-cutting measures because you add root tabs every 3 to 4 months. Just bury down the root tabs in the substrate, and they will slowly release elements to your live plants.

Can you use aquarium plant fertilizer in a fish tank?

Many people may wonder if there is any fertilizer safe for our fish. Primarily, read the label. Usually, the best aquarium plant fertilizers are made to use in a fish tank. If you do not add too much, your fish will only benefit from it. Dense vegetation means more places to hide, and fish will feel more comfortable, so using a fish tank plant fertilizer can only positively impact your animals.

Though, in the aquarium trade, some products can be used only in a planted aquarium. For instance, large quantities of aquarium plant fertilizer that contains copper or nitrogen can harm our livestock.

Fertilizing with carbon dioxide

CO2 injection is recommended, especially when you have a freshwater aquarium with intense light. Every aquatic plant needs carbon dioxide to perform photosynthesis. Traditional low-tech planted tanks can't get such results in plant growth as in tanks with CO2 regulators. The effects can be 5 to 10 times bigger. If you have slow-growing plants in your planted aquarium, additional carbon dioxide will stimulate them to grow faster and significantly impact their colouration. Some plants need CO2 injections, and growing them in planted tanks is impossible without them. An example of this would be the Eriocaulon cinereum.

If you want to read more about how a CO2 system can benefit your aquarium, click here.

Aquarium fertilizer- to buy or not to buy?

Aquarium plants need macro and microelements. They will reap the benefits and catch the viewer's eyes if you dose them correctly. But every tank is different. There are too many variables to give a dosing schedule that is universal for everyone. Tank size, type of plants, light intensity, the number of fish and their kinds are only examples of factors that really matter.

The best advice that can be said is to start low and go slow. Watch your aquarium and adjust your aquarium fertilizer. Take the recommendations from the manufacturer and take photos of your aquarium plants. That will be easier to compare if the aquarium fertilizer provides any consequences.