Description

Hesi CalMag 1 L - liquid calcium and magnesium supplement for soft water

CalMag by Hesi is a liquid mineral supplement that adds calcium and magnesium to watering water. It was developed for crops watered with soft, demineralized water, rainwater, or reverse osmosis (RO) filter water, which usually lacks these two elements.

Calcium builds cell walls, supports the plant's stable structure, and participates in signal transmission within tissues. Magnesium is a central component of chlorophyll, so when it is deficient, photosynthesis weakens and the leaves become pale and yellow. When supplied together, they help plants efficiently absorb other nutrients and maintain intensely green foliage.

The product balances the mineral content of soft water and can be used at every stage of cultivation - from seedlings to flowering. It is especially recommended for modern growing systems and under LED lighting, where plants' need for calcium and magnesium may be higher.

Key features

  • supplements calcium and magnesium in soft, distilled, and RO-filtered water
  • buffers soft water before adding base fertilizers
  • for growing in soil, coco (also for buffering coco growing media), and hydroponics
  • suitable for manual watering and automatic irrigation systems
  • for use during all stages of plant development
  • also contains iron chelate and molybdenum

Composition and NPK analysis

  • NPK 5-0-0 (5% total nitrogen)
  • 7.5% magnesium oxide (MgO)
  • 5.0% calcium oxide (CaO)
  • iron chelate and molybdenum

Application

Hesi CalMag supplements calcium and magnesium at every stage of cultivation when plants are watered with soft water, rainwater, or reverse osmosis water. It is useful for home plant collections, in greenhouses, and in gardens - anywhere water has a low mineral content, as well as when the first signs of calcium or magnesium deficiency appear on the leaves. It can be combined with base fertilizers in soil, coco, and hydroponic cultivation.

Directions for use

  • Soft water: add CalMag to the water until the electrical conductivity (EC) reaches 0.4-0.5 mS/cm; with soft tap water, use a correspondingly smaller amount depending on the starting EC
  • Distilled or RO water (EC 0): 3-4 ml per 5 L of water
  • 10 ml per 50 L of water raises the MgO level by 15 mg/L (approx. 9 mg/L Mg) and the CaO level by 10 mg/L (approx. 7 mg/L Ca)
  • 50 ml per 100 L of water raises the MgO level by 38 mg/L (approx. 23 mg/L Mg) and the CaO level by 25 mg/L (approx. 18 mg/L Ca)

Shake the bottle vigorously before use. With RO or very soft water, add CalMag first, before the base fertilizers. After mixing all ingredients, check the pH and EC of the prepared solution.

Safety and storage

Store in the original, tightly closed container in a cool, shaded place out of reach of children and animals. The product is not intended for consumption. Avoid contact with the eyes and skin.

Product information

  • Capacity: 1 L
  • Form: liquid concentrate
  • Type: calcium-magnesium supplement, NPK 5-0-0
  • Growing medium: soil, coco, hydroponics
  • Manufacturer: Hesi Plantenvoeding B.V., the Netherlands

Hesi CalMag in a 1 L bottle is a simple way to supplement calcium and magnesium wherever watering water is too low in minerals.

Product form

Hesi CalMag 1 L – calcium and magnesium supplement for soft water and RO

65,60 zł

    • Fast shipping within 24 hours
    • Premium quality

    Description

    Hesi CalMag 1 L - liquid calcium and magnesium supplement for soft water

    CalMag by Hesi is a liquid mineral supplement that adds calcium and magnesium to watering water. It was developed for crops watered with soft, demineralized water, rainwater, or reverse osmosis (RO) filter water, which usually lacks these two elements.

    Calcium builds cell walls, supports the plant's stable structure, and participates in signal transmission within tissues. Magnesium is a central component of chlorophyll, so when it is deficient, photosynthesis weakens and the leaves become pale and yellow. When supplied together, they help plants efficiently absorb other nutrients and maintain intensely green foliage.

    The product balances the mineral content of soft water and can be used at every stage of cultivation - from seedlings to flowering. It is especially recommended for modern growing systems and under LED lighting, where plants' need for calcium and magnesium may be higher.

    Key features

    • supplements calcium and magnesium in soft, distilled, and RO-filtered water
    • buffers soft water before adding base fertilizers
    • for growing in soil, coco (also for buffering coco growing media), and hydroponics
    • suitable for manual watering and automatic irrigation systems
    • for use during all stages of plant development
    • also contains iron chelate and molybdenum

    Composition and NPK analysis

    • NPK 5-0-0 (5% total nitrogen)
    • 7.5% magnesium oxide (MgO)
    • 5.0% calcium oxide (CaO)
    • iron chelate and molybdenum

    Application

    Hesi CalMag supplements calcium and magnesium at every stage of cultivation when plants are watered with soft water, rainwater, or reverse osmosis water. It is useful for home plant collections, in greenhouses, and in gardens - anywhere water has a low mineral content, as well as when the first signs of calcium or magnesium deficiency appear on the leaves. It can be combined with base fertilizers in soil, coco, and hydroponic cultivation.

    Directions for use

    • Soft water: add CalMag to the water until the electrical conductivity (EC) reaches 0.4-0.5 mS/cm; with soft tap water, use a correspondingly smaller amount depending on the starting EC
    • Distilled or RO water (EC 0): 3-4 ml per 5 L of water
    • 10 ml per 50 L of water raises the MgO level by 15 mg/L (approx. 9 mg/L Mg) and the CaO level by 10 mg/L (approx. 7 mg/L Ca)
    • 50 ml per 100 L of water raises the MgO level by 38 mg/L (approx. 23 mg/L Mg) and the CaO level by 25 mg/L (approx. 18 mg/L Ca)

    Shake the bottle vigorously before use. With RO or very soft water, add CalMag first, before the base fertilizers. After mixing all ingredients, check the pH and EC of the prepared solution.

    Safety and storage

    Store in the original, tightly closed container in a cool, shaded place out of reach of children and animals. The product is not intended for consumption. Avoid contact with the eyes and skin.

    Product information

    • Capacity: 1 L
    • Form: liquid concentrate
    • Type: calcium-magnesium supplement, NPK 5-0-0
    • Growing medium: soil, coco, hydroponics
    • Manufacturer: Hesi Plantenvoeding B.V., the Netherlands

    Hesi CalMag in a 1 L bottle is a simple way to supplement calcium and magnesium wherever watering water is too low in minerals.

    Frequently Asked Questions - FAQ

    Do you ship orders to the entire European Union?

    Yes, we ship to all countries in the European Union. The cost and delivery time depend on the destination country, the chosen shipping method, and current logistical conditions.

    Can I pay cash on delivery (COD)?

    Cash on delivery is available in selected European Union countries. Available payment methods are always displayed during the checkout process, depending on the delivery country.

    Where can I find sowing and cultivation instructions?

    Instructions and guides on sowing and plant care can be found in the product descriptions and on our blog, where we regularly publish educational materials. Additionally, we include a printed instruction manual with every order.

    Are the seeds sold legal and safe?

    Yes, all products offered by Mr.seed are legal and marketed in accordance with applicable regulations and the guidelines of phytosanitary institutions.

    Where do the seeds come from?

    Our seeds come from trusted producers and direct sources around the world. We collaborate with plantations, botanical gardens, and experienced seed collectors.

    How quickly are orders shipped?

    We ship most orders on the same or next business day. During busy periods, such as peak season or holidays, processing time may extend up to 72 hours.

    Where can I find answers to more questions?

    You can find an extensive database of answers on the full FAQ page, where we cover in detail topics such as orders, shipping, payments, cultivation, and products.

    👉 [Go to the full FAQ]

    Footer image

    © 2026 mr.seed, Shopify Technology

    • PL (PLN zł) PL (PLN zł)
    • English flag English flag
    • American Express
    • Apple Pay
    • Bancontact
    • BLIK
    • Google Pay
    • Klarna
    • Maestro
    • Mastercard
    • MB WAY
    • MobilePay
    • PayPal
    • Union Pay
    • Visa