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Nutrient deficiencies
Watching your plants can help you spot nutrient deficiencies and keep your aquarium healthy. Signs tend to appear sooner in aquariums with enough light and added CO2, where plants grow quickly. In slower-growing aquariums, changes can take longer to show.
Pay particular attention to fast-growing plants. A slow-growing plant such as Anubias may take up to two weeks to show a problem, while a fast-growing Hygrophila may show changes within a day or two.
Symptoms are clues rather than a diagnosis. Use them alongside water tests and checks of lighting, CO2 and circulation before changing your dose.
Mobile and immobile nutrients
Nutrient deficiencies can look very similar because minerals have several roles in a plant. One useful distinction is between mobile and immobile nutrients. Plants can move mobile nutrients from old leaves to supply new growth; nutrients that are harder to move can affect new growth first.
Examples of mobile nutrients include nitrate, phosphate and magnesium. Calcium and iron are less mobile. The location of the symptoms can therefore help narrow down the possible cause.
It is rarely as simple as matching one symptom to one nutrient. Several deficiencies can cause the same symptom, and a shortage of one nutrient can prevent the plant from taking up another. An obvious existing deficiency can also hide a developing one. Check the whole aquarium rather than relying on a single leaf.
Nutrient deficiencies table
Use these symptoms as a starting point and check your water parameters before changing the dose.| Description | Element | Possible issue |
|---|---|---|
| Old leaves turn yellowish/red | KNO3 (nitrate) | deficiency |
| Leaves become detached and develop small holes | KH2PO4 (phosphate) | deficiency |
| Yellowish spots on old leaves while the vein remains green | MgSO4 (magnesium) | deficiency |
| Yellowish areas on old leaves and yellowish edges on new leaves. Leaf dies | K2SO4 (sulphate) | deficiency |
| Yellowish edges on new leaves, damage (deformations) / death of new growth | Ca (calcium) | deficiency |
| Black/brown leaves, plant is dying | KH2PO4 (phosphate) | surplus |
| New leaves turn yellow | S (sulphur) | deficiency |
| White growing tips, but veins remain "green" | Fe2 (iron) | deficiency |
| Yellowish spots between the veins, starting at the edge and tip of the leaf | Zn (zinc) | deficiency |
| Dead yellowish leaves between the veins | Mn (manganese) | deficiency |
| Dead leaf tips and spotty edges | Cu (copper) | deficiency |
| New growth dies | B (boron) | deficiency |
| Yellow spots between leaf veins, and brown areas against the leaf margin | Mo (molybdenum) | deficiency |
| Plant remains small, little to no growth, white deposits (calcium) on leaves | CO2 (carbon dioxide) | deficiency |
| Fish gasp for air | CO2 (carbon dioxide) | surplus |
| Sluggish fish combined with no plant growth | O2 (oxygen) | deficiency |
| Plant stops growing / black roots | Substrate | replace |
CO2 and water movement
- Air stones and strong surface movement can drive CO2 out of the aquarium. Consider this when checking your CO2 supply and filter setup.
- Lighting and CO2 need to be in balance. Too much CO2 can be a problem, especially when plant growth is limited by light. Watch your fish carefully when changing the CO2 supply.
Check the substrate
Gas bubbles rising from the substrate or blackened plant roots can indicate a problem with the substrate or nutrient layer. Inspect its condition and consider whether it needs attention or replacement.
To prevent a build-up of debris, clean accessible areas of the substrate during water changes. A substrate cleaner can help remove dirt without disturbing the whole aquarium.
Water temperature
When the temperature is too low for the plants you keep, growth can stop and the plants may eventually die. Temperatures that are too high can lead to smaller leaves and longer gaps between the leaves. Check the temperature requirements of your plants.
Lighting
Plants need light for photosynthesis. Insufficient light or ageing fluorescent tubes can leave plants weak, with small, pale leaves. Growth nearer the surface may be less affected.
You can read more in the Easy-Life article about plant growth and lighting (Dutch).