Ionic Cal-Mag Pro - Calcium & Magnesium Fix for Hungry Plants
Best for: growers in coco, RO, or soft-water hydro systems who are seeing pale new growth, interveinal yellowing, or want to head off cal-mag problems before they start.
Our thoughts
We rate Cal-Mag Pro as one of the easiest ways to stop calcium and magnesium deficiency wrecking a grow before it gets going. It's a Growth Technology product, so it's formulated properly rather than being some vague "boost" bottle, and a little goes a long way. At this price it's a sensible add to any feeding schedule running coco, RO water, or soft tap water.
Ionic Cal-Mag Pro is a concentrated calcium and magnesium supplement from Growth Technology, the UK manufacturer behind the wider Ionic nutrient range. It's built to correct and prevent Ca/Mg deficiency in fast-growing plants, particularly during heavy flowering when calcium and magnesium uptake is at its highest. The formula carries an NPK of 3.8-0-0 with 5.6% calcium, 4.01% magnesium and 0.15% chelated iron, plus amino acids and humic acids to help the plant actually use what it's given rather than just diluting the feed.
Because it's designed as an add-on rather than a base feed, it works alongside any brand of nutrient - coco, soil or hydro - and is particularly useful for growers using reverse osmosis or soft tap water, where calcium and magnesium are naturally in short supply.
How it compares
Cal-Mag correctors are a crowded shelf, but Ionic's version holds its own against the big names.
- Costs less per litre than Advanced Nutrients Cal-Mag Xtra while covering the same Ca/Mg/Fe bases
- Sits alongside CYCO Cal-Mag+ and Canna Cal Mag Agent as one of the standard supplements most grow shops stock for RO or coco growers
- Comes in a 300ml size that the premium brands mostly skip, so you're not forced into a full litre just to try it
Not a flashy product, but it does the one job it's there for at a lower cost than most of the alternatives.
Usage guidance
Dosage
Add 0.5ml per litre as a preventative measure alongside your normal feed, or 1ml per litre if you're already seeing deficiency symptoms such as pale new leaves or brown spotting on older leaves.
Correcting a deficiency
Once new growth comes back green and healthy, drop back to the preventative 0.5ml/L rate rather than staying on the corrective dose long-term.
Compatibility
Works alongside any base nutrient brand - coco, soil, or hydro - since it's a supplement rather than a complete feed.
Technical specifications
- Brand: Growth Technology (Ionic range)
- NPK: 3.8-0-0
- Calcium (Ca): 5.6%
- Magnesium (Mg): 4.01%
- Iron (Fe, chelated): 0.15%
- Additional ingredients: amino acids, humic acids, organic plant extracts
- Format: liquid concentrate
- Sizes available: 300ml, 1 litre, 5 litre
- Preventative dose: 0.5ml/L
- Corrective dose: 1ml/L
Who this is for
- Coco coir growers who need extra Ca/Mg on top of their base feed
- Growers using reverse osmosis or soft tap water
- Anyone seeing pale new growth or brown spotting during heavy flowering
- Budget growers who want a proven cal-mag fix without paying premium-brand prices
Our take
Cal-Mag Pro isn't a product you buy to get excited about, it's one you buy so you stop having a problem. It does exactly that, and it's priced sensibly enough that there's no reason to run RO water or coco without a bottle of something like this on the shelf.
One we sell a lot of for new growers who've just worked out their tap water isn't cutting it.
