A & B Nutrients: The Ultimate Australian Guide to 2-Part Hydroponic Feeding (2025)

Why Two Bottles?

Calcium nitrate is a diva, the moment it touches phosphates or sulphates at high concentration it binds up, falls out of solution and your plants miss dinner. By packing Ca and micro-trace goodies in Part A and packing P, K and magnesium in Part B, manufacturers guarantee 100 % solubility once diluted in your reservoir. The result? Stable EC/pH curves and a feed chart that actually works.

Big Benefits

• Hard-water resilience: Many Aussie municipal supplies hover at 120–200 ppm CaCO₃. A/B systems let you dial calcium back when tap water already brings plenty to the party.
  
• Heat-proof mixes: Warm res temps accelerate precipitation. Separate parts safeguard solubility during scorching summers.
  
• Coco & RDWC flexibility: Whether you’re running high-coco blends or deep-water culture, 2-part lines handle both without extra bottles cluttering the grow room.
  

Different Types of Base Nutrients (And Who They’re For)

Not all base nutrients work the same way, even when they look similar on the shelf.

Single A & B formulas

These use the same Part A and Part B from seedling through harvest. You simply increase or decrease strength as plants grow.
✔ Great for beginners
✔ Fewer bottles and simpler feeding
✔ Works well in most hydro systems

Grow & Bloom A & B formulas

These separate vegetative and flowering nutrition. Grow formulas are higher in nitrogen, while bloom formulas focus more on potassium and phosphorus.
✔ Better control for flowering plants
✔ Popular with fruiting crops like tomatoes and chillies
✔ Slightly more complex feeding schedule

One-part nutrients

Usually lower concentration and designed for ease of use.
✔ Simple mixing
✖ Less flexibility
✖ Often need higher volumes per feed

Organic or hybrid bases

Designed for biological systems rather than sterile hydro.
✔ Suitable for living media
✖ Not ideal for recirculating systems
✖ Can clog lines or create bio-film in reservoirs

If you’re running DWC, NFT, or recirculating coco, a quality mineral A & B nutrient remains the most reliable option.

What’s Actually in Your A & B Nutrients

Most quality A & B nutrients look similar, but the label tells you a lot about how they’ll perform.

You’ll usually see:

• Macronutrients: nitrogen, phosphorus, potassium, calcium, magnesium
  
• Micronutrients: iron, manganese, zinc, copper, boron, molybdenum
  

Micronutrients are often listed as chelated. This simply means they’re bonded in a way that keeps them available to plants, even when pH drifts slightly.

Why this matters:
Non-chelated micros can drop out of solution, especially in hard water or higher pH ranges. Chelation helps prevent deficiencies and improves consistency.

You’ll also notice calcium is almost always in Part A, while sulphates and phosphates are in Part B. Keeping them separate prevents unwanted reactions in the bottle—and in your reservoir.

Choosing the Right Line

Pro Tip: Run each brand’s feed chart at 80 % strength for the first two waterings.

If you’re comparing two-part systems to more complex multi-bottle programs, The Complete 2026 Guide to Hydroponic Nutrients & Additives in Australia breaks down boosters, micros and when they’re actually worth adding.

Mixing 101 – Step-by-Step

1. Fill the tank with room-temp water, note start EC.
   
2. Add Part A, stir 30 sec until clear.
   
3. Add Part B, stir again. Never pour both concentrates into the same measuring jug.
   
4. Check EC – aim 1.2-1.6 mS (cm) in early veg, 1.6–2.4 mS in mid-bloom for most plants.
   
5. pH last, target 5.8–6.0 in coco, 5.6–5.8 in DWC.
   
6. Top-up regularly with pH-balanced water; re-set full tank every 14 days to dodge salt creep.
   

For strawberry growers, nutrient ratios shift as plants move from veg to fruit set—our Hydroponic Strawberry Nutrition: Ultimate 2025 Australian Guide maps exact EC, pH and A/B doses for every phase.

Product Round-Up & Brand Matrix

Need boosters? Pair your base with our hydroponic additives to crank up resin density without juggling extra base bottles.

Simple EC-First Mixing Example

A common mistake is following millilitre amounts without checking EC.

Here’s a safer approach:

1. Fill your reservoir with water
   
2. Measure starting EC (example: 0.3 EC)
   
3. Add Part A, mix well
   
4. Add Part B, mix well
   
5. Measure EC again
   
6. Stop when you reach your target EC (not the bottle’s max rate)
   
7. Adjust pH last
   

For example, if your target EC is 2.0 and your water starts at 0.3, you’re really adding 1.7 EC worth of nutrients, not the full amount listed on the label.

This method reduces overfeeding and keeps results consistent across different water sources.

Water Quality Matters More Than You Think

Before you even add Part A or Part B, the quality of your water plays a big role in how well nutrients perform.

Across Australia, tap water can vary a lot. Some areas have very soft water, while others are high in calcium, magnesium, or bicarbonates. This affects both your starting EC and how easily plants absorb nutrients.

What to check first:

• Measure your starting EC before adding nutrients
  
• If your tap water is already above 0.4 EC, you’ll usually need to reduce nutrient strength
  
• Very hard water can cause nutrient lockouts over time, especially with calcium and iron
  

For growers running RO or rainwater, your starting EC will be close to zero. That gives you full control, but it also means your A & B nutrients are doing all the work of supplying minerals.

Quick tip:
Always build nutrients from your starting EC, not from zero. Two growers using the same feed chart can get very different results if their water sources are different.

This is one of the most common reasons new growers struggle—even when following instructions correctly.

Common Crop pH & EC Guide

While feed charts are a great starting point, different plants naturally prefer different ranges.

Use this as a guide, not a rulebook:

Leafy Greens (lettuce, spinach, herbs)

• pH: 5.8 – 6.2
  
• EC: 1.2 – 1.8
  
• Tip: Keep EC lower to avoid tip burn
  

Tomatoes & Cucumbers

• pH: 5.8 – 6.3
  
• EC: 2.0 – 3.0
  
• Tip: Increase EC gradually during flowering
  

Strawberries

• pH: 5.5 – 6.0
  
• EC: 1.6 – 2.2
  
• Tip: Sensitive to overfeeding
  

Chillies & Capsicums

• pH: 5.8 – 6.3
  
• EC: 2.2 – 3.0
  
• Tip: Stable feeding gives better fruit set
  

Always watch the plant, not just the numbers. Healthy growth tells you more than a meter ever will.

Troubleshooting Cheat Sheet

And if your plants still show weak stems or heat stress despite perfect EC, Silica for Plants in Australia: The No-Nonsense Guide to Stronger, Happier Crops explains how silica plugs the structural gaps A&B nutrients don’t cover.

FAQs

Do I need extra Cal-Mag with A&B?
Only if your tap reads under 70 ppm or you’re running LED-heavy rooms. Otherwise Part A plus Aussie water has you covered in most cases.

How long do mixed nutrients stay stable?
7-10 days in outdoor conditions where the reservoir is exposed to elements, up to 14 days in optimal conditions.

Ready to Feed Like a Pro?

Check the full Hydroponic Nutrients collection and score free shipping when your cart tops $250. Questions? Hit the team on 1800 983 006 – we’ll give you the straight answer, no fluff.

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