CalMag in Hydroponics – Why Calcium & Magnesium Matter
Calcium and magnesium are two of the most important secondary nutrients in hydroponics and soil growing. While often overlooked, they’re vital for plant strength, nutrient uptake, and chlorophyll production. Their availability is largely influenced by the hardness of your tap water, so supplementing correctly with CalMag is essential for achieving strong, healthy crops and bigger harvests..
Hard Water vs. Soft Water – Does It Matter?
Yes, it matters a lot.
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Soft Water (common in western and northern UK):
Low in calcium and magnesium, typically with EC below 0.4
➤ Use a CalMag supplement to increase available nutrients -
Hard Water (common in eastern and southern UK):
Higher EC, usually above 0.8, naturally contains more calcium and magnesium
➤ Only use CalMag if a deficiency is visible
For ultimate water control, we recommend using a Reverse Osmosis system, like the Growmax Reverse Osmosis System, to remove all minerals and start with 0 EC water. Then, add your CalMag supplement to dial in the exact nutrient levels your plants need.
Spotting Calcium and Magnesium Deficiencies
Calcium Deficiency:
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Weak stems
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Slow growth
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Yellow or brown patches on new growth
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Irregular leaf shape with sharp brown edges
Unlike magnesium, calcium is immobile, meaning it cannot move from older leaves to new growth, so deficiencies show up at the top of the plant.
Magnesium Deficiency:
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Yellowing between leaf veins (interveinal chlorosis)
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Rusty brown spots on older leaves
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Poor photosynthesis and slower energy production
Magnesium is mobile and will be pulled from older leaves to support new shoots, leading to visible lower-leaf symptoms first.
Benefits of Using a CalMag Supplement
Using a dedicated CalMag supplement, such as those from Shogun, Canna, Plant Magic, DutchPro, or Biobizz, offers multiple advantages:
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Supports chlorophyll production for greener, more vibrant plants
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Strengthens cell wall structure for firmer stems and leaves
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Improves photosynthesis and sugar transport
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Enhances root uptake of other nutrients
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Buffers against nutrient excess or lockout
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Boosts resistance to pests and diseases
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Promotes better flowering and fruit formation
A well-balanced CalMag level increases nutrient efficiency across the board.
How to Test Water Hardness
You can try the simple “bottle test” at home using liquid soap and a clear bottle:
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Fill a bottle halfway with tap water
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Add a few drops of soap and shake
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Lots of bubbles = soft water; few or no bubbles = hard water
This won’t give an exact EC, so for precision, check with your local water supplier or use an EC meter for accurate readings.