Introduction to Fertilizers for a Planted Aquarium

A modern planted aquarium cannot be conceived without fertilizers. Plants consume nutrients from the water and if fertilizer supply stops plants start to die.
Many people have heard about fertilizers for aquarium plants but do not know exactly what these fertilizers are and why are needed in a planted aquarium.

Fertilizers are concentrated solutions of macronutrients and micronutrients that are added to the water to support plant growth.

In nature (rivers, lakes) fertilizers are produced naturally but in aquarium, which is a closed system, macronutrients and micronutrients are consumed quickly by plants and in order to avoid plant death we must introduce fertilizers every day.

• Macronutrients: Calcium, Carbon, Hydrogen. Magnesium, Nitrogen, Oxygen, Phosphorus, Sulfur and Potassium.
• Micronutrients (trace elements): Boron, Copper, Manganese, Molybdenum, Chlorine, Nickel, Iron and Zinc.

Macronutrients and Micronutrients are essential for plant growth and only the quantity varies, macronutrients are required in larger quantities and micronutrients are required in limited quantities.

Lack of micronutrients and macronutrients usually generates some problems for plant growth and in the best case plant growth stops and in the worst case plants will die. Now if you know what represents the lack of nutrients you have to know that also excess of micro and macro nutrients brings nothing good.

In the next part we`ll discuss about the influence of every nutrient and we will start with Micronutrients (trace elements):


• Boron
Boron regulates the action of hormone growth and it is located in cellular membrane. Lack of boron leads to slow growth and new leaves are deformed.

Manganese has many functions in plant growth and the most important it is the activation of the enzymes used for photosynthesis and chlorophyll making. Manganese deficiencies can be easily confused with the iron deficiencies because both ( Fe and Mn) deficiencies have the same symptoms, leaves gradually turn white while veins remain green. For Mn deficiencies the leaf will have only few white spots but in most cases the manganese introduced when you are changing the water it is enough, tap water contains enough quantities of manganese.

Molybdenum is a very important micronutrient and when a lack of molybdenum is recorded the plant growth will stop and photosynthesis is seriously affected. The molybdenum deficiency is manifested by low growth rate and the leaves are pale green. Tap water contains molybdenum but if that it is not enough you will find molybdenum in tablets.

Zinc is an important micronutrient and it is absorbed by plants through roots and leaves. Zinc deficiency makes plants to remain small and the plant growth is stopped and plant will die.

Perhaps Iron it is the most important micronutrient and it is used in chlorophyll synthesis, enzyme production and respiration.
Because iron it is an important plant fertilizer it can be found in substrate and all the aquatic fertilizers include iron in their composition. Iron deficiency will make young leaves to appear pale and yellowish with green veins, usually old leaves are normal.
Please remember that tap water does not contain iron that can be used by plants because plants absorb only divalent white iron.
Iron deficiency solutions: Dennerle E15 FerActiv, Seachem Flourish Iron, Easy Life Ferro, MICROBE LIFT Iron, EHEIM Ferrous fertilizer.

iron fertilization for aquarium plants

We are talking about chlorine in the form of chloride ions and not gas because it is extremely dangerous to fish and plants. Usually an aquarium will never have a chlorine deficiency because is present in sufficient quantities in tap water.
As you can see above some micronutrients have a greater role in physiological processes of plants, others micronutrients have less role but it is important to have all micronutrients in aquarium.


Carbon is the most important macronutrient and is obtained by plants from carbon dioxide (CO2). As is already known plants use the carbon resulting from the process of photosynthesis when CO2 is broken into Oxygen (O2) and Carbon. Oxygen is used by plants in small quantities compared with carbon and that is the reason you see oxygen bubbles coming from leaves.
Because CO2 is gas the amount of CO2 in the water is influenced by the water surface agitation.
For plants the easiest way to obtain CO2 is from the surrounding water and that means we have to introduce CO2 into aquarium from an external source directly into water using a CO2 diffuser or reactor.
Carbon deficiency can be easily observed because plants have slow growth and leaves are small and on leaves you can observe white deposits. Carbon excess is not bad for plants but for fish is very dangerous.
Liquid carbon: Easy Life Easy Carbo, Seachem Flourish Excel .

Until now you knew that plants consume carbon dioxide and eliminate oxygen during photosynthesis, but when plants have no light the process of photosynthesis is reversed, plants consume oxygen and remove carbon dioxide.
Plants need only a small amount of oxygen and you must avoid a high concentration of oxygen because nutrients (Iron especially) bind with oxygen leading to generalized deficiency.
At night it is the only moment when the level of oxygen drops because plants start to use oxygen for respiration.
Even if fish and plants use oxygen during night the level of oxygen is not dropping dangerously because water has some surface agitation and the gas exchange is provided.
In a planted aquarium is not necessary to add oxygen through an air pump.

Nitrogen is very important in transforming inorganic substances into organic matter through photosynthesis. Plants do not take nitrogen in its “crude” gas state but obtain by several forms: nitrite, nitrate, ammonium, ammonia. In case there is a nitrogen deficiency plants grow very small and leaves turn yellow.
Nitrogen deficiency solutions: Seachem Flourish Nitrogen, Tropica Plant Growth Specialised Fertiliser,  MICROBE LIFT Bloom & Grow Nitrogen, Easy Life Nitro.

easy life nitro

Like many other macronutrients phosphorus is essential in plant development, being responsible with root and stems growth. Plants do not take phosphorus in its “crude” state but absorb phosphate through roots.
Because phosphate is also in fish food are rarely cases when phosphate deficiency is present. In natural conditions phosphate levels are 0.005-0.02 mg/liter and in freshwater aquarium values of 1-3mg/liter are quite common. Low levels of phosphate are not a problem and it is recommended to have low level of phosphate because certain levels of phosphate can create algae bloom. Algae prefer phosphate values to be over 0.03 mg/liter, to avoid such values you must not overfeed your fish and the number of fish from your aquarium must be correlated with the aquarium water volume.
A deficit of phosphate can occur in aquariums with low fish and many plants and usually the symptoms for phosphate deficiency are: leaves darker than normal and the growth rate is low.
Many aquarists use a version of Redfield Ratio to establish the values for nitrate and phosphate, the ratio for N and P it is 16:1.
Phosphorus deficiency solutions: Seachem Flourish Phosphorus, Easy Life Fosfo, MICROBE-LIFT Phosphorous.

Potassium is a key factor in plant growth and in a planted aquarium should not be neglected. Potassium deficiency is observed quickly because the edges of the leaves become yellow.
Potassium excess leads to deficiencies of calcium and magnesium and in some cases reacts with iron causing iron deficiency.
Potassium deficiency solutions: Seachem Flourish Potassium, MICROBE LIFT Potassium

• Calcium
Calcium is responsible for the division and plant growth by activating certain enzymes also it is a key element in maintaining cell permeability. In almost all aquariums are enough quantities of calcium and this macronutrient should not be added artificially.
Calcium deficiency: New leaves are deformed while the existing leaves do not change shape.

Magnesium is an important macronutrient for all plants and regulates many enzymatic processes. In a freshwater aquarium the ideal level of magnesium it is 5-25 mg/liter. Usually when you do the water change you will add magnesium because tap water contains this macronutrient also magnesium is present in many liquid fertilizes. Too much magnesium in water will inhibit potassium uptake and in many cases potassium deficiency is caused by magnesium excess.
Magnesium deficiency: Leaves turn yellow while the veins remain green.

Micronutrients and macronutrients absorption it is influenced by the PH of the water and every aquarium is a particular case and  if you have a successful recipe for a tank it does not mean you can apply that recipe to another tank and to be sure the success is guaranteed.
To have success with your aquarium you must have a balance between LIGHT – FERTILIZATION – CO2, any imbalance will induce algae bloom.
Lack of from water should be supplemented by CO2 from an external source otherwise plants will not grow and will appear all kinds of imbalances because we add fertilizers but without CO2 plants are not able to consume the added fertilizers.
On the market you find many types of fertilizers and before you start to use it you must read the instructions and add fertilizer according to these instructions. If after you do water tests you notice that the nutrients level it is too low you can increase the amount of fertilizer and repeat tests.
Some tips for plant fertilization:
 make water tests, especially for beginners it is a must
 do not add fertilization from the first day.
 do not use air pumps
 stop the fertilization if you use UV lamps


Last modified onFriday, 18 December 2015 20:41
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