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    Deficiency symptoms in aquatic plants

    Correctly interpret growth damage

    In the article "Fertilizing a planted aquarium" we already presented the most important nutritional ressources for proper growth, which are, in short, the factors light, carbon, micro- and macronutrients. According to Liebigs Law of the Minimum, a complete nutritional coverage is essential for the plants to grow vitally.
    If aquarium plants suffer from inhibited growth or even dying tissue, there is usually a lack of nutrients or imbalances at hand. Not uncommonly, this appears in combination with an increased growth of algae.
    This article deals with deficiency symptoms in aquatic plants. In practice, these damage patterns can not be clearly or easily assigned to a particular nutrient, since they are very similar to one another and different defects can still look similar. Nonetheless, the following list should provide an overview for the aquatic plant aquarist, sorted by the importance of the individual nutrients.

    1. CO2

    CO2 fertilization

    In the case of any deficiency in aquatic plants, you should first consider carbon dioxide intake before dealing with the other nutrient factors. Most of the damage patterns listed below, such as yellow leaves or crippled growth, can also be caused by a carbon deficiency. A CO2fertilization is essential for healthy plant growth. In a more densely planted aquarium, the CO2 saturation should be at a level of about 20 to 30 mg/l. This should be permanently monitored, using an appropriate drop checker. It is important, that you regularly change the indicator fluid every four to six weeks to keep the test working correctly.
    Only after ruling out a lack of CO2, the other topics can be addressed.

    2. Macronutrients

    Macronutrients are nutrients that are needed by plants in larger quantities. These include above all the elements potassium, phosphorus and nitrogen, but also magnesium. We now go into detail on the most important macronutrients and typical deficiency symptoms.


    nitrogen deficiency

    Nitrogen (N) can be absorbed by aquatic plants in various forms: ammonium, urea, nitrate. For the determination of the nitrate content, usually only water tests capable of indicating nitrogen in the form of nitrate (NO3) are available. Optimal concentrations are at around 10 to 25 mg/l NO3. Unfortunately most common water tests for nitrate are not easily readable and may cause measuring errors. For indicating nitrate, we recommend a higher-quality test, which is easier to read, such as the nitrate test from Macherey & Nagel.

    Yellow leaves

    A typical nitrogen deficiency phenomenon is an overall yellowing of the plant, especially in the older leaves. But also increasingly smaller new leaves or crippled growth can be an indication of a nitrogen deficit. For some plant species, a distinctly reddish hue may occur. An increased occurance of green thread algae, fuzz algae or hair algae are not rare when the aquarium is lacking in nitrogen. It is possible to push the nitrogen content with liquid fertilizers such as Aqua Rebell Makro Spezial N or Advanced GH Boost N without notably influencing other nutritional parameters. With a simultaneous potassium deficit, the Aqua Rebell Makro Basic Nitrat is a good option.


    phosphate deficiency

    This element can be determined by use of common water tests as a concentration of phosphate (PO4). Indications of phosphorus (P) deficiency are readily diagnosed on fast-growing stem plants. Typical is a very slow growth and decreasing shoot tips.

    small shoot tip

    Some aquatic plants may turn dark or violet. Frequently, phosphorus deficiency causes increased spot algae. For a planted aquarium, phosphate concentrations of about 0.1 to 1 mg / l PO 4 are recommended. However, a certain content does not have to be permanently measurable and permanently maintained. Phosphate is quite reactive and can therefore interact with other nutrients such as iron. In addition, plants can store this element really well. In this respect, a weekly push fertilization with a phosphate fertilizer like Aqua Rebell Makro Basic Phosphat has proven in practice.

    Crippled growth in comparison

    Easy to see in direct comparison: Below a healthy Rotala, above a specimen with crippled growth. Often, this is an indication of a lack of macronutrients, such as phosphorus.


    potassion deficiency

    Typical for a lack of potassium (K) are perforated leaves or dying leaf tissue (necroses). In the beginning, these are only recognizable as small, black dots, but then grow up to visible holes, which are partially outlined in yellow or black. Similar to nitrogen deficiency, yellow leaves may be associated with reduced growth. Optimal potassium concentrations are around 5 to 10 mg / l. As a suitable potassium water test we recommend the Macherey-Nagel Visocolor ECO Kalium. This element can be precisely pushed with a pure potassium fertilizer like Aqua Rebell’s Makro Basic Kalium. If phosphorus and nitrogen are lacking as well, a combined macronutritional fertilizer like Makro Basic NPK or Estimative Index is preferred.


    A Rotala with notable necroses (holes, black tissue). A cause of this might be a lack of potassium.


    Typical necroses on a Java fern.


    magnesium deficit

    Magnesium (Mg) plays an important role in photosynthesis, because it is a decisive element of the plant’s green (chlorophyll). A deficit is often shown by a pale or yellow discolouration of older leaves, but the leaf veins usually remain green. Magnesium is still a rather underrated nutrient in plant aquariums. If you want to get more involved with the topic, we recommend the article about the calcium-magnesium ratio.

    magnesion deficiency

    This Bucephalandra develops yellowish leaves, while the leaf veins remain green. This may be due to a lack of magnesium.


    Micronutrients are elements, the plants only need in small amounts (for the most part only as trace elements) for their growth. These include primarily iron, but also other metals such as copper, boron or manganese. By using a complete iron fertilizer, all micronutrients are usually covered.


    iron deficit

    Due to a lack of iron (Fe) less chlorophyll is formed in the plants in their new shoots. An iron deficiency is therefore easily identified at the shoot tips of fast-growing stem plants. The rich leaf green fades, and the young plant parts grow in a yellow to white color (chlorosis).

    helle Triebspitzen

    This stem plant clearly shows lighter shoot tips, due to an iron deficiency.

    With a serious iron deficit additional stunted growth and black, dying leaf tissue (necrosis) may occur. The deficiency symptoms can be easily remedied by adding a little more complete iron fertilizer. Alternatively, you can target the iron content with a special fertilizer like Aqua Rebell Mikro Spezial Eisen.
    Ideal iron concentrations for a plant aquarium are given as 0.05 to 0.1 mg/l Fe, which can be determined with a suitable water test. However, it is not absolutely necessary to permanently maintain a measurable iron value. Especially when using mildly chelated complete fertilizers such as Aqua Rebell Mikro Spezial Flowgrow iron can only be indicated right after fertilization. After a couple of hours, iron might not even be determinable anymore. The nutrient is absorbed very quickly by the aquatic plants due to its easy availability. So long as no typical deficiency symptoms show, it is not necessary to increase fertilization with a complete iron fertilizer. On the contrary, over-fertilization may even promote the growth of red algae such as staghorn- or beard algaen. But these can be removed by appropriate measures.


    Good to see in comparison: A leaf belonging to a houseplant with chlorosis (left). A lack of magnesium or iron may be the reason here.

    Other trace elements

    As a rule complete iron fertilizers don’t just cover the iron requirements of the aquatic plants, but also their needs in all other vital trace elements. In aquaristic practice, therefore, these other micronutrients and their deficiency symptoms are not given special attention. Lack of carbon, iron or macronutrients is much more likely and should therefore be addressed first.

    4. Light

    ADA Aquasky LEDs

    A lack of light is rare in a coordinated system. However, a lack of light can be a cause of poor plant growth, but reviewing the nutrients from points 1 to 3 should have a much higher priority. The lighting requirements of the plants should naturally match the technical conditions of the aquarium. One deficiency symptom may be, for example, extremely slow growth. Many light-hungry plant species such as most of the stem plants, but also some ground cover, like to etiolate with a lack of lighting. In this case, the plant grows with very long internodes, that is, wide distances between two stalk nodes (nodes), towards the top towards the light. An intensification of the lighting ensures a more compact growth, but then it is also important to adjust the supply of carbon dioxide and the micro- and macro elements. The light increase acts like a catalyst on plant growth and entails a higher nutrient consumption. Otherwise this might cause an imbalance and result in increased algae growth. Often, however, the choice of location for a particular group of plants is not entirely optimal. Poor illumination of certain areas of the aquarium or excessive shading by other plants or by the decoration are common causes. An improvement of the location situation may provide remedy for the affected plant group.

    The right perspective

    Rotala from above

    Rotala frontal vie

    The same stalk of a Rotala viewed from different angles: From above, through the water surface (upper picture) and through the front pane (bottom picture). Good to see is the change in the red color, which appears more magenta in the lower picture. The use of RGB lighting (here: Twinstar LED Light ) further enhances this effect. Both photos were taken under the same conditions (color temperature: 3650 Kelvin).

    When considering deficiency symptoms in aquatic plants you should be aware, that certain optical factors have influence on the result. It may happen that you see deficiency symptoms in your plants, even though there’s no reason. The colour of the light source has an influence on how you perceive the colours of your aquatic plants, e.G. the leaf green. Light sources with daylight spectrum of about 6500 Kelvin are neutral. Some pure white LEDs, on the other hand, make bright greens look very pale and whitish. This could be misinterpreted as chlorosis. By contrast, LED illuminators with an increased RGB content, for example, enhance reds, which look much less spectacular under more neutral light.Also important is the angle of incidence at which a submerged plant is examined. Seen from above through the water surface, light green tones also look much paler than looking at the same plant through a side pane. A different point of view can suddenly give the impression of a chlorosis, which is actually not present or at least not very pronounced.