Fish and plants can suffer from deficiency symptoms which are not recognized as such. A fish, for example, can get a kind of ulcer which is caused by iodine deficiency. Holes in plants are often not caused by a deficiency but quite simply by plant-eating fish, such as long-whiskered cat fish or loaches. Therefore it makes sense to read up a little on deficiency symptoms:

In fish

As the term implies it can lead to a deficiency in certain substances. As with humans it is mostly diet-related. The exception is water. For us it is part of our nutrition, but for fish it is their living medium. Therefore the composition of the water is extremely important. Deficiency symptoms can arise as a result of substances missing from the water.

Holes in the body, mainly in the head area

This can be the hole in the head disease (Hexamita, Spironucleus), which, in connection with flagellates, can lead to a mineral deficiency. Then the fish extracts endogenous tissue and holes form. This almost always occurs in very soft, low-mineral water.

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Holes in head and body (marine fish)

Often in connction with a discolouration of some body parts: it is caused by a deficiency of minerals and trace elements which often occurs after an unbalanced feeding with garden vegetables (lettuce, cucumber). Marine fish (e.g. surgeonfish) are algae eaters and ingest an unbelievable variety and quantity of minerals and trace elements through the algae. Lettuce and cucumber are practically free of minerals and trace elements! A feeding of lettuce and cucumber every now and then might be good but should be done in moderation. For algae eaters especially designed foods as basic food prevent deficiency symptoms:

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Ulcerous growths in the throat area

Caused by iodine efficiency.

Remedy: either feeding iodiferous food or adding iodine to the water.

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A deficiency of certain minerals or nutrients can also arise in plants. This can be noticed just by looking at the plants. In the following you can see the possible manifestations of various deficiency symptoms in aquarium plants:

Stagnating growth

When plants which always grew beautifully and suddenly, for no apparent reason significantly stagnate in growth, you need to research the cause. As when a car breaks down, you may not think of looking at the petrol gauge, but according to the ADAC it is helpful in 30 % of all cases.


Remedy: Please check whether your CO2 cylinder still contains any CO2 or needs refilling. Did you forget the liquid fertilisation? Did you accidentally adjust the timer for the lighting so that the plants are now just getting 2 hours light a day?

Nitrate quantities of over 50 mg/l lead to growth inhibition in many plants, although nitrate in smaller concentrations acts as nutrients. Can also lead to crypt melt.


Partial water change and JBL BioNitratEX and to insert fast-growing plants.

Good nitrate consumers include Cabomba, Hygrophila and Limnophila species.

Extreme temperatures (< 18 °C or > 29 °C), extreme pH values (< 6.5 or > 8.0), as well as extreme hardness (KH < 4° dKH or > 10 ° dKH) hinder the plant growth. For remedies and the correction of water values see Analiza wody Online-laboratorium . Especially “hard” anti-algae agents considerably hamper plant growth and can even lead to plant deaths (which are closely related to the algae).


Switching over to JBL Algol (Ostrożnie stosować biocydy. Przed użyciem zawsze przeczytać oznaczenie i informację o produkcie. Zarejestrowany w Federalnym Urzędzie Ochrony i Medycyny Pracy o numerze BAUA N-19236.) when there are algae problems.

Light green leaves

Iron deficiency leads to light green, yellowish, glassy or pale leaves. The set point for the iron content ( JBL Fe Żelazo Test ) is 0.05 - 0.2 mg/l. To raise the iron content JBL PROFLORA Ferropol or JBL PROSCAPE Fe +MICROELEMENTS are most suitable. If you already use a fertiliser and the iron test still doesn’t indicates sufficient values, this can have the following reasons: Your fertiliser contains iron but in a form (Fe2+) which gets oxidised from the oxygen in the water (reacts with the oxygen) and so becomes unusable for the plants or your fertiliser doesn’t contain any iron.

Bulging of the leaf veins

When the leaf nerves are particularly prominent on the leaf colour this could be caused by a potassium deficiency. With the potassium test ( JBL K Potas Test ) you can immediately check if it really is a potassium deficiency.

Remedy: by adding a potassium containing fertiliser, such as JBL PROFLORA Ferropol , JBL PROSCAPE K MACROELEMENTS you remedy the deficiency and the leaf veins will not bulge again.

Long stems, few leaves

Often easily recognisable on stem plants. The plans probably don’t receive a full spectrum, but an excess of reddish light. This reddish light creates a strong cell enlargement. On stem plants this looks unsightly because the stem grows quickly and the distance between the leaves increases. This then looks as if the plant has too few leaves.

Remedy: avoid lamps with very reddish spectrum. Use lighting with daylight or sunlight full spectrum instead ( JBL SOLAR TROPIC and JBL SOLAR NATUR ).

Lack of light

Plants always move towards the light. In strong light the plant can grow lower than in weak light, where it has to move upwards to the light. So the growth of a plant species can vary. If you insert stem plants too close together the lower plants will get not enough light and putrefaction processes will start.

Remedy: don’t press stem plants together into the soil, but insert them individually with a little distance. For the lighting requirements you can use the ProScape Kalkulator światła .

Holes in leaves

Contrary to expectations this is not a sign of deficiency; your fish just love to eat plants.

Remedy: check your fish stock! There are probably some plant eaters amongst them. Common culprits are long-whiskered cat fish (Ancistrus) or loaches (Botia). Once you have caught the culprits, swap them for other species. For instance, long-whiskered cat fish can easily be replaced by dwarf suckers (Otocinclus).

Crypt melt

Often arises from changes in maintenance conditions and relocation. The only remedy is to provide stable conditions and to reduce the nitrate value below 50 mg/l.

Plants become mushy and decay after a while

Some popular aquarium plants are actually not underwater plants but marsh plants which can survive some time - but not too long! - under water. Many water plants (e.g. Amazon sword plants) are cultivated emersed (above water) and initially shed the leaves they grew above water when they are submerged (put under water). All that can help here is patience and the purchase of pure underwater plants.

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