Plant deficiency guide
Magnesium Deficiency
Also called low magnesium, low GH
Older leaves yellow between the veins while the veins stay green.
TL;DR, Magnesium Deficiency
Magnesium is mobile, so like iron it yellows between the veins, but on old leaves rather than new. The veins stay green while the tissue between them fades to yellow, starting low on the plant. It turns up most in soft or RO water with little added magnesium, and it usually travels with a low general hardness. Raise magnesium with a GH booster or remineraliser that includes it, or a small Epsom salt dose, and keep GH in a sensible range.
What you see
Older, lower leaves yellow between the veins while the veins stay green, the same interveinal pattern as iron but on old growth instead of new. New tips look fine. It often shows across several older leaves at once in soft water.
What causes it
- Soft or RO water with little magnesium
- Low general hardness overall
- A calcium-to-magnesium balance skewed too far toward calcium
- Heavy uptake in a fast-growing tank
How to fix it
- Raise magnesium with a GH booster or remineraliser that includes calcium and magnesium.
- Or dose a small amount of Epsom salt, which is magnesium sulphate.
- Check that GH sits in a workable range, a few dGH for most planted tanks.
- Aim for a calcium to magnesium ratio around 3:1 to 4:1.
Keep it from coming back
Remineralise RO water with a product that includes magnesium, and keep GH in range rather than letting it drift toward zero. Test GH now and then in soft-water tanks.
Easy to confuse with
Iron looks the same, interveinal yellowing, but iron hits new leaves and magnesium hits old ones, so check where it starts. Nitrogen fades old leaves evenly rather than between the veins.
Plants that show it first
Compare against a species you keep. These plants flag magnesium trouble early or clearly:
Frequently asked questions
Direct answers to the questions search engines and AI assistants surface most often about this species.
Is it iron or magnesium?
Both yellow between the veins. Iron affects new leaves, magnesium affects old leaves. Where it starts tells you which.
How much Epsom salt should I add?
A small dose goes a long way. Start low, re-test GH, and adjust. It is easier to add more than to reverse an overdose.
What Ca to Mg ratio should I aim for?
Around 3:1 to 4:1 calcium to magnesium is a common target when remineralising RO water.