Canna Calmag Agent — Water Conditioner & Calcium-Magnesium Supplement for Soft Water Growing
Best for: Growers in soft water areas, RO water users, and anyone running coco or inert media who wants to prevent nutrient deficiencies
Our thoughts
Water quality varies wildly across the UK, and soft water can catch you out fast. Canna Calmag Agent is the straightforward fix — it's a highly concentrated calcium and magnesium supplement that buffers soft water to the right EC level and prevents the deficiencies that tank your crop. One we recommend constantly for growers using RO or soft tap water.
Canna Calmag Agent is a concentrated water conditioner that raises the calcium and magnesium levels in soft or reverse osmosis water to prevent secondary nutrient deficiencies. It works across all growing media and pairs seamlessly with Canna base nutrients. The product is designed to raise your water EC to around 0.4mS/cm — the sweet spot for hydroponic growing — ensuring your plants get consistent mineral balance regardless of where you live in the UK.
How it compares
Canna Calmag Agent sits at the professional grower tier of calcium-magnesium supplements.
- More concentrated than most alternatives — 1ml per litre is all you need
- Dual action: water conditioner and deficiency corrector in one bottle
- Specifically formulated for UK water hardness variations
- Works with all media types (soil, coco, hydroponics, rockwool)
- Integrates perfectly with Canna Terra and Coco nutrient ranges
Competitors like General Hydroponics CALiMAGic and Terra Aquatica offer similar results, but Canna Calmag is the UK market leader and designed specifically around regional water profiles.
Usage guidance
For soft water or RO water growers
Fill your reservoir with water at room temperature. Add Canna Calmag Agent at 0.1–0.5ml per litre depending on your starting water hardness. Target EC of 0.4mS/cm. Wait 24–48 hours before making pH adjustments — the solution naturally fluctuates during this time, so patience saves headaches.
Practical example
Using 8 litres of soft water? Add roughly 8–10ml of Calmag Agent to bring it to 0.4 EC. Then add your regular Canna base nutrients on top. Job done.
With hard water (EC above 0.8)
If you're unlucky enough to have very hard tap water, use reverse osmosis to clean it down to near zero EC first, then use Calmag Agent to raise it back to 0.4. Sounds extra, but it's the cleanest approach.
In coco or inert media
Because coco binds calcium and magnesium differently to soil, this becomes essential. Calmag Agent prevents lockout and keeps nutrient uptake strong throughout the cycle.
Technical specifications
- Type: Concentrated calcium-magnesium solution
- Available sizes: 1 litre and 5 litre bottles
- Dosage rate: 0.1–0.5ml per litre of water
- Target EC: 0.4mS/cm
- Calcium to magnesium ratio: 2:1 (optimal for plant uptake)
- Nitrogen content: 5.9% (supports deficiency correction)
- Storage temperature: 10–30°C, protect from heat, frost, and direct sunlight
- Storage: Keep sealed in original container only
- Compatibility: All growing media and base nutrient systems
Who this is for
- Growers in soft water areas (much of Scotland, Wales, Northern regions)
- Anyone running reverse osmosis systems
- Coco coir growers (where calcium-magnesium lock-out is a real risk)
- Hydroponic and drip irrigation setups where EC control matters
- Experienced growers building their own nutrient schedules
- Budget growers wanting to prevent expensive crop failures from deficiencies
Particularly useful if you live in a soft water region and have had yellowing leaves, browning leaf edges, or stunted growth — classic signs your water needs mineral buffering.
Our take
This is proper, essential kit if you're growing with soft water or RO. It's concentrated enough that a 1-litre bottle lasts for ages, integrates seamlessly with Canna's existing nutrient lines, and solves the single biggest problem soft water growers face: mineral deficiency.
Worth picking up if you're setting up a coco system or running RO water. Costs a fraction of what a crop failure costs. Good time to buy while stock lasts.
