How to Mix MasterBlend (½ Dose) for a 25-Litre Hydroponic Container

Overview

MasterBlend is a widely used three-part hydroponic nutrient system consisting of:

1. MasterBlend 4-18-38
2. Calcium Nitrate
3. Magnesium Sulfate (Epsom Salt)

Using a half-strength (½ dose) nutrient mix is recommended for:

• Seedlings and young plants
• Recently transplanted crops
• Leafy greens in early growth stages
• Plants showing nutrient sensitivity

This guide explains exactly how to mix a ½ dose for a 25-litre container.

Full-Dose Reference (25 L Container)

For context, a full-strength solution for 25 litres uses:

Half-Dose Measurements (25 L Container)

A half dose is simply 50% of the full dose:

✅ These measurements are accurate for 25 litres of water.

Mixing Order (Very Important ⚠️)

Always mix nutrients one at a time to avoid precipitation and nutrient lockout.

Step-by-Step Mixing

1. Fill container with 25 L of water
   • Use room-temperature water
   • Let tap water sit 12–24 hours if chlorinated
2. Add Magnesium Sulfate (Epsom Salt) – 8 g
   • Stir until fully dissolved
3. Add MasterBlend 4-18-38 – 8 g
   • Stir thoroughly until water is clear
4. Add Calcium Nitrate – 4 g
   • Stir again until fully dissolved

🚫 Never mix dry nutrients together before adding to water

Target EC & pH (½ Dose)

Typical targets for a half-strength solution:

• EC: 0.6 – 1.0 mS/cm
• PPM (500 scale): ~300 – 500
• pH: 5.8 – 6.2

Adjust pH after all nutrients are mixed.

When to Use Half Dose

Use this solution for:

• Seedlings (after first true leaves)
• First 1–2 weeks after transplanting
• Lettuce, spinach, and other leafy greens (early stage)
• Stress recovery (heat, root damage, overfeeding correction)

Once plants are established, gradually increase to ¾ dose, then full dose if needed.

Common Mistakes to Avoid

❌ Mixing Calcium Nitrate before MasterBlend
❌ Adding nutrients to very cold water
❌ Guessing measurements (use a scale)
❌ Ignoring EC and pH checks

Pro Tip 🌱

If you regularly mix nutrients:

• Pre-weigh dry nutrients into labeled containers
• Keep a mixing log (date, EC, pH, crop)
• Rinse measuring tools between nutrients

Summary

For a 25-litre container (½ dose MasterBlend):

• 8 g MasterBlend 4-18-38
• 4 g Calcium Nitrate
• 8 g Magnesium Sulfate

Mixed in the correct order, this solution provides gentle, balanced nutrition for young and sensitive hydroponic plants.