Magnesium Deficiency (Mg)
Magnesium is the literal core atom of the chlorophyll molecule, just like iron is for our blood. Without it, the plant cannot absorb light. Since Magnesium is one of the two primary minerals determining General Hardness (GH), soft water or unbalanced hard water can easily lead to severe deficiency. It is a highly mobile element, meaning the plant will strip it from old leaves to supply the new growth.
Plant profile
Resolution Difficulty
Observe and distinguish
Identification and context
Signs and distribution
Interveinal Chlorosis on OLD Leaves
The absolute classic sign of Magnesium starvation is interveinal chlorosis: the fleshy part of the leaf turns pale white or yellow, while the veins remain stark, dark green. Crucial diagnostic tip: Iron deficiency causes the exact same symptom, but on NEW leaves. Magnesium deficiency always strikes the OLD, bottom leaves first.
Drooping and Curling
In severe cases, the margins of the older leaves curl severely downwards (often called 'cupping' or 'hooking') due to structural breakdown before falling off.
Affected tissue and growth
Interveinal Chlorosis on OLD Leaves
The absolute classic sign of Magnesium starvation is interveinal chlorosis: the fleshy part of the leaf turns pale white or yellow, while the veins remain stark, dark green. Crucial diagnostic tip: Iron deficiency causes the exact same symptom, but on NEW leaves. Magnesium deficiency always strikes the OLD, bottom leaves first.
Drooping and Curling
In severe cases, the margins of the older leaves curl severely downwards (often called 'cupping' or 'hooking') due to structural breakdown before falling off.
Physiology or exposure
Magnesium is the literal core atom of the chlorophyll molecule, just like iron is for our blood. Without it, the plant cannot absorb light. Since Magnesium is one of the two primary minerals determining General Hardness (GH), soft water or unbalanced hard water can easily lead to severe deficiency. It is a highly mobile element, meaning the plant will strip it from old leaves to supply the new growth.
Verify before intervening
Confirmation and decisions
Differential diagnosis
Compare sign distribution, leaf age, mechanical damage, emersed-to-submersed adaptation, algae, pests and multiple concurrent deficiencies.
How to verify
Confirm with a photographic timeline, repeated measurements and one controlled change at a time; an isolated leaf sign does not automatically identify the cause.
Proportionate actions
Management and monitoring
What to do now
Stabilize light, CO₂, temperature and water quality; remove only decaying tissue. Avoid concentrated corrections or several simultaneous changes.
Controlled correction
Dose Magnesium Sulfate (commonly known as Epsom Salts) or a balanced commercial GH booster (like Seachem Equilibrium). Aim to add about 5 to 10 ppm of Magnesium to the water column, which will correspondingly raise your GH by roughly 1 to 2 degrees. Cut away severely yellowed old leaves as they will not recover.
New-growth response
Always remineralize RO water with a high-quality GH powder to establish a steady 3:1 or 4:1 Calcium-to-Magnesium ratio. If you use tap water, look up your local water report; if it is calcium-heavy, you will need to actively dose Epsom Salts on a weekly basis to maintain balance.
Prevention
Always remineralize RO water with a high-quality GH powder to establish a steady 3:1 or 4:1 Calcium-to-Magnesium ratio. If you use tap water, look up your local water report; if it is calcium-heavy, you will need to actively dose Epsom Salts on a weekly basis to maintain balance.
When to escalate
Escalate if deterioration is rapid, involves the rhizome or stem, produces foul odor, or coincides with animal distress or detectable ammonia/nitrite.