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How to Fertilize a Planted Aquarium - Aquascaping Guide

What do aquatic plants need to grow in the aquarium? 
This is a question that every initiate to Aquascaping asks himself when reading about the subject. of aquarium plants and their fertilization. We would like to briefly explain which components are crucial to the healthy growth of aquarium plants.


Every plant needs light for photosynthesis. Initiates to the Planted Aquarium They often hear the following advice when their plants are not growing well: "Add more light." However, this may not be the solution to the problem in all cases. Different species of plants have different requirements when it comes to light intensity. There are plants that are easy to maintain, that do not need much light; Red-leaved plants do need much more light (and nutrients). The amount of light will be the most important element and from which we must start to condition the following points.


When fertilize your aquarium with CO2, you supply your plants with an element that is generally not found in aquariums without a CO2 injection equipment. The addition of CO2 is an absolute must if you want to grow large numbers of fast growing plants and create clumps, even undemanding plants accelerate their growth, and your health improves significantly when carbon dioxide is added. There should be no planted aquarium without a CO2 injection system. There are solutions for all budgets, biological CO2 systems from low to medium priced for beginners or somewhat more expensive but much more efficient systems that use refillable pressurized carbon dioxide bottles, you can also make contributions of liquid carbon, in the form of fertilizer, but for short seasons or in low amounts.


This point we are going to talk about liquid fertilizers. This is one aspect of Planted Aquariums which unfortunately is neglected. NPK represents the elements nitrogen (N), phosphorus (P) and potassium (K), that plants need, and in relatively large quantities. The nitrogen and phosphorous compounds that plants can absorb can be created in the aquarium by the activity of microorganisms, which break down fish droppings, dead plant parts, and fish food debris, however, these sources are usually insufficient especially in aquariums with many plants, with a very strong light or with CO2 injection. Plants need more than they get this way. And the most crucial macro element, potassium, is not even part of the waste cycle in an aquarium. Still, plants require it. Many manufacturers offer NPK fertilizers, generally in the form of liquid fertilizer, this is not the best option, the ideal is to pay each nutrient separately, being able to pay each element as the plants need, these amounts we can know thanks to the water tests or with something more than experience observing the deficiencies that aquarium plants show. If we fertilize more fertilizer than the plants need, these surpluses will be used by the algae to develop and we will run the risk of algae infection.

Planted Aquarium Fertilizers - Aquascaping


In addition to many other trace elements, plants mostly require iron. This element is crucial for green leaf color and especially for red leaf plants. The most recommended is to pay daily to cover the consumption of plants and avoid over fertilization and the appearance of unwanted algae.

These four factors form the basis of a well-balanced system and healthy plant growth.

Aquascaping image made by Sergio Maestre CEO Premium Buces


This we think is the best way to pay a Planted Aquarium. The Law of the Minimum, describes how plant growth is limited by resource constraints. Plants need many different nutrients, the so-called essential nutrients, to grow healthy. If only one If these nutrients are lacking, plant growth will be inhibited, even if all other essential nutrients are available and in abundance.
This also works for all other resources, such as light and CO2 in amounts suitable for the respective plant species. The scarcest resource always limits the growth of plants and therefore it is called limiting factor.

We have named the four main factors for the good growth of aquarium plants in the previous points: Light, carbon (in the form of CO2), macronutrients and micronutrients.

If aquatic plants show signs of deficiencies, even along with intensive algae growth, the reason is usually an imbalance in the supply of nutrients. Therefore, giving them more light and CO2 will not result in better plant growth if there is a shortage of another specific nutrient such as nitrogen or iron for example.

As a countermeasure, nutritional gaps must be identified and closed. To do this, two things are important: First, the water parameters must be verified with the corresponding water tests, and second, you should try to interpret the symptoms of visible deficiencies in the plants. This you can know thanks to the guides and explanatory images on the subject, and knowing them you will be able to identify certain nutritional deficits. For this, we recommend our article “Deficiencies in Aquarium Plants - Nutritional deficiencies and solutions". In that article we explain it in more detail.


Taking into account the previous points, the amount of fertilizer that we must pay will be what the plants need and we can know this through the natural indicators of the aquarium (bioindicators), to the aquarium tests, and to the sudden appearance of algae, the most recommended is to pay daily in small amounts before a large amount of fertilizer once a week, we must avoid surpluses that algae can use to grow.

They can be used as a tool any of the calculators that are on the Internet or that offer the same manufacturers of fertilizers, With this we can get a little idea of ​​where to start paying. However, these calculated subscriber recommendations only serve as a first clue. As an aquarium evolves, the fertilizer dose should be adjusted regularly. The consumption of an aquarium They will not be the same newly installed, when it is already running for a few months and we have a large mass of plants or just after pruning. We recommend a weekly water change of 50% to avoid accumulation of polluting substances and accumulation of a specific nutrient.

As we have previously named, there are no standard amounts to pay in an aquarium in general. These amounts depend rather on the individual circumstances of each aquarium. However, certain amounts of nutrients can be described for guidance within the following ranges:

10 to 25 mg / l nitrate (NO3)
5 to 10 mg / l potassium (K)
0,1 to 1 mg / l phosphate (PO4)
0,05 to 0,1 mg / l iron (Fe)
> 10 mg / l magnesium (Mg)

In general, a distinction should be made between nutrients whose concentration must be maintained at a certain level at all times (including CO2, nitrate, potassium, and magnesium) and nutrients that do not require a constant level (such as iron and phosphate). ). The concentration of the latter may not be detectable by the water tests after a few days of having paid. This does not have to have negative consequences, since plants can store some nutrients like phosphate pretty well. If there are no deficiency symptoms and growth defects in plants, it is not necessary to maintain permanently measurable iron and phosphate concentrations.


Aquatic plants consume nutrients, but, depending on the nutrient it is, at quite different speeds and quantities. In our experience, nitrogen consumption in a densely planted aquarium with many fast growing stem plants is quite high, while other macroelements such as potassium and magnesium are not consumed as much.

To determine nutrient intake, they are necessary tests for the water that are of quality and easy to read. Testing for parameters like nitrate, phosphate, and iron is especially important. If necessary, you can also include potassium and magnesium tests.

To calculate consumption, measures these relevant parameters at the beginning and end of a week. The difference between the two values ​​establishes the corresponding weekly consumption of nutrients. To determine the average daily consumption, simply divide the weekly consumption by seven. It can be done in fewer days and divided by the same number of days.

If you use any fertilizer during the measurement period there is no problem, you can still calculate the nutrient intake using the method described above. In this case, you will have to subtract the fertilizer you have added from the calculated weekly consumption. If the result is zero, the fertilization and nutrient requirements are perfectly adjusted and balanced against each other. At any value greater than zero, the plant's nutrient intake is still slightly higher than what you add to your fertilizer routine, so you will need to increase the amount of fertilizer appropriately. On the other hand, if the weekly consumption value is negative, the amount of fertilizer is greater than the consumption and should be adjusted as necessary.

If you use tap water, or mix this mains water with osmosis water. The parameters of the water can vary greatly depending on the area in which you live. For this it is very important to know exactly the parameters of the tap water and include them in the subscriber calculations.

Other articles of interest may be:
How to Eliminate Aquarium Algae - Causes and Most Effective Treatments

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