Fertilizers & nutrients
by Biobizz
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Biobizz Calmag is a 100% organic calcium and magnesium supplement that prevents and corrects mineral deficiencies in soil, coco, and hydro grows. If you're running RO water, soft tap water, or growing in coco coir, your plants are almost certainly short on these two minerals — and the symptoms (yellow leaves, stunted growth, weak stems) show up fast. Buy Biobizz Calmag to slot straight into your existing feed schedule and keep your plants structurally sound from seedling to harvest.
Calcium and magnesium are essential secondary macronutrients that most water sources fail to supply in adequate quantities. They don't appear on your standard NPK label, but without them, your plants fall apart — sometimes literally. Calcium is the backbone of cell walls. Without enough of it, new growth comes in twisted, leaf tips curl, and blossom end rot turns your fruit to mush before it's even ripe. Magnesium sits at the centre of every chlorophyll molecule. Strip that out and photosynthesis grinds down, starting with interveinal yellowing on older fan leaves that creeps upward through the canopy.
The problem? Most water sources don't carry enough of either mineral. Reverse osmosis water has virtually zero. Soft tap water in cities like Amsterdam often tests below 50 ppm calcium — a figure consistent with municipal water quality reports from Dutch water utilities. Even decent soil mixes get depleted by mid-bloom when your plants are drinking hardest. We've seen growers blame their lights, their pH, their genetics — when the actual issue was a small dose of calcium and magnesium they never added.
Biobizz Calmag addresses this with a formula that's fully organic and compatible with living soil, coco, and hydro setups. No synthetic chelates, no EDTA — just plant-available calcium and magnesium that your roots can absorb immediately. It pairs directly with Biobizz Grow and Biobizz Bloom without throwing off your nutrient ratios, and the dosing is low enough (0.3–1 ml per litre) that you're not going to accidentally lock anything out.
Biobizz Calmag is a 250 ml organic liquid concentrate dosed at 0.3–1 ml per litre across all growing media and stages.
| Spec | Value |
|---|---|
| Brand | Biobizz |
| Product | Calmag |
| Type | Calcium and magnesium supplement |
| Formulation | 100% organic liquid |
| Bottle Size | 250 ml |
| SKU | HS2826 |
| Compatible Media | Soil, coco, hydro, light mix |
| Usage Stage | Vegetative through harvest |
| Prevention Dose (Coco/Hydro) | 0.5–1 ml per litre |
| Prevention Dose (Soil) | 0.3–0.8 ml per litre |
| Pairs With | Biobizz Grow, Biobizz Bloom |
Calcium deficiency shows as distorted, curling new growth with brown rust-like spots, while magnesium deficiency presents as interveinal yellowing on older lower leaves. Catching either early saves your harvest — and we see both of these walk through the door in photos at least twice a week.
Calcium deficiency hits new growth first. Look for distorted, curling leaf tips on the upper canopy. Brown spots that look like rust appear on younger leaves, and in severe cases the growing tips die off entirely. Stems feel hollow or weak when you squeeze them gently. If you're growing tomatoes or peppers alongside your main crop, blossom end rot (that black, mushy patch on the bottom of the fruit) is the classic calcium red flag.
Magnesium deficiency targets older leaves first — the plant cannibalises its lower fan leaves to feed new growth. You'll see yellowing between the veins while the veins themselves stay green, creating a striped pattern that's hard to miss. Left unchecked, the yellow turns brown and the leaves drop. During heavy flowering, magnesium demand spikes and this deficiency can appear seemingly overnight.
One honest limitation worth mentioning: Calmag corrects calcium and magnesium shortfalls specifically. If your plants show symptoms that don't match these patterns — like overall pale yellowing (nitrogen) or purple stems (phosphorus) — the issue lies elsewhere. Calmag isn't a cure-all, and stacking it on top of a different deficiency just raises your EC without fixing the problem.
Add Biobizz Calmag to your water first, before any other nutrients, at 0.3–1 ml per litre depending on your medium and growth stage.
The 250 ml bottle lasts between 250 and 500 litres of feed water at standard prevention doses, making it one of the longer-lasting supplements per millilitre we stock. A single bottle covers roughly a full small tent grow from start to finish. If you're running a larger setup — say a 120x120 tent with 4–6 plants — you'll burn through it by mid-bloom and want a backup on hand. Order a second bottle upfront if you're running more than four plants.
One thing we'd flag: growers using hard tap water (above 200 ppm) rarely need Calmag at all. Your water already carries plenty of calcium and magnesium. Adding more on top can push your EC too high and cause nutrient lockout — the exact opposite of what you're trying to achieve. If you don't know your water hardness, pick up a cheap TDS meter before you start supplementing. It's a 10-second test that saves weeks of headaches.
We'd pick Biobizz Calmag over synthetic alternatives every time for organic grows. Synthetic calmag products (like those using calcium nitrate) work fine in hydro, but they introduce nitrogen forms that can disrupt organic soil biology. Biobizz keeps your microbial life intact, which matters if you're running living soil or using other Biobizz products like Top-Max or Bio-Heaven.
Complete your Biobizz feed schedule with Biobizz Grow for vegetative nutrition and Biobizz Bloom for flowering. If you're building a full organic setup, get Bio-Heaven (amino acid stimulant) alongside Calmag — it pairs well and helps improve nutrient uptake across the board. Running coco? Grab a pH meter and TDS meter alongside your Calmag — in coco, precision is everything.
Biobizz Calmag is the only fully organic calmag option in the Biobizz range, using no EDTA chelates and requiring roughly half the dose of typical synthetic alternatives.
| Feature | Biobizz Calmag | Synthetic Calmag (typical) |
|---|---|---|
| Organic Certified | Yes — 100% organic | No — uses EDTA chelates |
| Compatible with Living Soil | Yes | Can disrupt microbial life |
| Nitrogen Added | Minimal | Often contains calcium nitrate |
| Dose Range | 0.3–1 ml per litre | Typically 1–2 ml per litre |
| Best For | Organic grows, Biobizz feed schedules | Hydro and coco with synthetic nutrients |
| pH Stability | Gentle — minimal pH shift | Can raise pH noticeably |
It depends on your water. If you're using soft tap water (below 100 ppm) or RO water, yes — soil alone won't provide enough calcium and magnesium through a full grow cycle. If your tap water is hard (above 200 ppm), you likely don't need it.
Yes. Calmag is a standalone calcium and magnesium supplement that works with any nutrient line. That said, it's specifically formulated to complement the Biobizz range, so you'll get the most consistent results keeping everything in the same family.
Existing damage won't reverse — brown spots and dead leaf tissue are permanent. But you should see healthy new growth within 5–7 days of correcting the deficiency. If nothing improves after 10 days, check your pH first. Calcium locks out below 5.5.
Yes. Excess calcium locks out potassium, magnesium, and iron. Excess magnesium locks out calcium. Stick to the recommended 0.3–1 ml per litre range and monitor your runoff EC. If it climbs above 2.5, flush with plain pH-adjusted water before your next feed.
It works in hydro, but keep in mind it's an organic product. In recirculating systems, organic compounds can break down and affect reservoir stability. It's best suited for drain-to-waste hydro, coco, or soil setups. For recirculating DWC or NFT, a mineral-based calmag may be more practical.
At a prevention dose of 0.5 ml per litre, one 250 ml bottle makes 500 litres of feed water. For a small tent with 2–4 plants, that's roughly one full grow cycle. Larger setups or deficiency correction doses will go through it faster — budget for 2 bottles if you're running 6+ plants.
Always add Calmag first, especially with RO water. This raises your baseline mineral content before you introduce other nutrients. Adding it after can cause calcium to bind with phosphates in your base nutrients and precipitate out of solution.
Last updated: April 2026
