Macronutrients are the nutrients aquarium plants use in large amounts, nitrogen (N), phosphorus (P) and potassium (K), together called NPK, while micronutrients are those needed only in tiny traces, chiefly iron plus manganese, zinc, boron and other trace elements. Plants need both: macros build the bulk of leaves, stems and roots, and micros power the enzymes and pigments that keep growth healthy and colourful. A complete all-in-one fertilizer such as Sunken Garden Green supplies both in balance. This guide explains what each nutrient does, the symptoms of running short, and when you might dose macros and micros separately.
Understanding macro and micro nutrients is the key that unlocks confident fertilising, once you know what each does, deficiency symptoms stop being a mystery.
Macronutrients vs micronutrients at a glance
The macronutrients explained
Nitrogen (N) is the engine of leafy growth plants use more of it than any other nutrient. Shortage shows as older leaves yellowing and dropping. Phosphorus (P) drives root development, energy transfer and flowering; a shortage stunts growth and can darken or spot leaves. Potassium (K) builds strong stems and regulates plant processes; its classic deficiency sign is pinholes and ragged edges in older leaves. These three, NPK are the headline numbers on any fertilizer. A potassium top-up like Seachem Flourish Potassium is a common fix for leaf-hole problems.
The micronutrients explained
Iron (Fe) is the most important micronutrient it is essential for chlorophyll and brings out rich greens and vivid reds. Iron shortage shows as pale or yellow new leaves. The other traces — manganese, zinc, boron, copper, molybdenum are needed in minute amounts but are vital for enzymes and healthy new growth. Because they are used in traces, they are easy to overlook, yet a micronutrient shortage stalls growth just as surely as a macro shortage. Read the iron story in detail in aquarium iron fertilizer & deficiency.
Macro and micro deficiency symptoms
| Symptom | Likely nutrient | Type |
|---|---|---|
| Older leaves yellow & fall | Nitrogen | Macro |
| Stunted growth, dark/spotty leaves | Phosphorus | Macro |
| Pinholes & ragged leaf edges | Potassium | Macro |
| Pale/yellow NEW leaves | Iron | Micro |
| Twisted, deformed new growth | Calcium / boron | Macro/Micro |
| General slow growth | Overall - dose all-in-one | Both |
A key clue: problems on old leaves usually mean a mobile macronutrient (N, P, K) the plant is moving to new growth; problems on new leaves usually mean an immobile micronutrient (iron, calcium). Full diagnostic in signs of nutrient deficiency.
Do you dose macros and micros together or separately?
Short answer: Together (as an all-in-one) for most tanks; separately only on high-tech CO2 tanks.
For low-tech and most planted tanks, a single all-in-one fertilizer that contains both macros and micros is simplest and works beautifully. High-tech aquascapers running CO2 sometimes dose macros and micros on alternate days, because in concentrated form some nutrients (notably iron and phosphate) can bind and precipitate if dosed together. That alternating approach is part of the EI dosing method. In a normal all-in-one at tank concentration this is not a practical problem.
Recommended products for macro & micro nutrition
Sunken Garden GreenMacros + micros in one 
Flourish PotassiumMacro (K) top-up 
Flourish AdvanceGrowth enhancer
An all-in-one like Sunken Garden Green covers both groups; add a single-nutrient supplement only to correct a specific deficiency. Browse the Aquarium Fertilizer collection.
India-specific note on calcium & magnesium
Calcium and magnesium are technically secondary macronutrients. In much of India the tap water is hard, meaning it already carries plenty of calcium and magnesium, so most Indian aquarists do not need to add them and can focus their fertilising on NPK and iron. If you use RO or very soft water, you may need a remineraliser to supply calcium and magnesium. Knowing your local water hardness helps you fertilise efficiently.
Frequently asked questions
What are macronutrients in aquarium fertilizer?
The nutrients plants use in large amounts nitrogen, phosphorus and potassium (NPK), plus calcium, magnesium and sulphur.
What are micronutrients in aquarium fertilizer?
Trace nutrients needed in tiny amounts chiefly iron, plus manganese, zinc, boron, copper and molybdenum.
What is the difference between macro and micro fertilizer?
Macro fertilizer supplies NPK in larger quantities; micro fertilizer supplies iron and trace elements in small quantities. Plants need both.
Do I need to dose macros and micros separately?
Only on high-tech CO2 tanks. For most tanks, a single all-in-one containing both is simpler and works well.
Which nutrient causes leaf holes?
Potassium deficiency causes pinholes and ragged edges in older leaves.
Which nutrient causes pale new leaves?
Iron (a micronutrient) deficiency causes pale, yellow or translucent new growth.
Why are my old leaves yellowing?
Usually nitrogen deficiency the plant moves nitrogen from old leaves to new growth, so old leaves yellow first.
Is iron a macro or micronutrient?
Iron is a micronutrient needed only in traces but it is the most important micronutrient for green and red colour.
Does an all-in-one fertilizer have both macros and micros?
Yes, a complete all-in-one contains both the macronutrients NPK and the micronutrients iron and trace elements.
Can I overdose micronutrients?
Yes, because they are needed in traces, micros (especially copper) can harm sensitive livestock if grossly overdosed. Follow the label.
Do I need to add calcium and magnesium?
Usually not in hard-water areas (common in India), as tap water supplies them. Soft or RO water may need a remineraliser.
What is the NPK ratio for aquarium plants?
There is no single ratio; balanced all-in-one fertilizers are formulated to suit typical planted tanks. Adjust only if symptoms point to a specific shortage.
Why do macros and micros get dosed on alternate days?
In concentrated high-tech dosing, iron and phosphate can bind together. Alternating avoids this. It is not an issue at normal all-in-one tank concentrations.
How do I know which nutrient my plants lack?
Read the symptoms: old-leaf problems point to macros (N, P, K); new-leaf problems point to micros (iron) or calcium. See our deficiency guide.
What is the easiest way to supply both macros and micros?
Use a complete all-in-one fertilizer such as Sunken Garden Green, it supplies both in one bottle.
Cover both nutrient groups easily with an all-in-one from the Aquarium Fertilizer collection or the Sunken Garden range. See also the complete fertilizer guide and deficiency signs.
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