Mixing Nutrient Solutions
Mixing Nutrient Solutions
Accurate nutrient mixing keeps minerals available, prevents lockout, and protects roots from burn. Replace the whole tank regularly (weekly works well for most growers) rather than endlessly topping up. The sections below pull everything together: pH, CF, hard vs soft water, element availability, meter guides, feed schedules, and the exact steps to mix a tank correctly.
pH Management
pH measures how acidic or alkaline your solution is. Plants absorb minerals best in a slightly acidic range. Keep this front of mind every time you mix a feed — it’s your reference point for nutrient availability.
Target Range
- Good pH: 5.6 – 6.8
- Optimum pH: ~6.2
Use a calibrated digital pH meter (e.g. Aqua Master pH Pen). Check after mixing nutrients and adjust with pH Down/Up in small amounts.
Element Availability Across pH
At ~pH 6–6.5, the “big three” (N, P, K) and key secondaries (Ca, Mg, S) are widely available, while most traces (Fe, Mn, B, Cu, Zn, Mo) also sit in their usable bands. Drift too alkaline and iron/manganese availability falls; too acidic and calcium/magnesium uptake suffers.
CF / EC Control (Nutrient Strength)
CF (Conductivity Factor) or EC shows how much dissolved mineral is in your tank — i.e., the strength of your feed. It should be your second key reference after pH to avoid under/overfeeding.
Typical CF Targets
- Cuttings & seedlings: CF 6–8
- Vegetative growth: CF 8–12
- Flowering/fruiting: CF 12–16
Measure with a calibrated CF/EC meter (e.g. Bluelab Truncheon). Record readings so you can repeat success from batch to batch.
Hard or Soft Water?
Hard water has more dissolved calcium/magnesium (often visible as limescale); soft water has less. Choose a nutrient line formulated for your water type, or use an RO filter in very hard areas.
How to Check
- Fill a bucket with tap water and leave it to stand for 24 hours (room temperature, chlorine dissipated) or use Ecothrive Neutralise to instantly dechlorinate water.
- Take baseline readings with calibrated meters:
| pH Reading | CF Reading | Recommended Feed Type |
|---|---|---|
| 7.8 or above | 8 or above | Hard Water Feed |
| 7.7 or below | 7 or below | Soft Water Feed |
Quick Guide to Meter Readings
Baseline CF varies with water hardness. Use this as a simple reference when aiming for quarter/half/three‑quarter/full strength feeds.
| Tap Water | ¼ Strength | ½ Strength | ¾ Strength | Full Strength | |
|---|---|---|---|---|---|
| Typical CF in hard water | 8 | 12 | 16 | 20 | 24 |
| Typical CF in soft water | 2 | 6 | 10 | 14 | 18 |
Feeding Schedule by System (Guide)
Use the strengths below as a week‑by‑week starting point. Always watch plant response and adjust in small steps.
| Stage → | Rooting Cuttings & Starting Seeds | Vegetative Growth | Flowering/Fruiting Growth | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| Week → | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 |
| NFT | ¼ | ½ | ¾ | Full | ¾ | ½ | |||||
| Flood & Drain | ¼ | ½ | ¾ | Full | ¾ | ½ | |||||
| Hydro Pots | ¼ | ½ | ½–¾ | ¾ | ¾ | ½ | |||||
| Coco | ¼ | ½ | ½–¾ | ¾ | ¾ | ½ | |||||
| All‑Mix / well‑fertilised compost | Water | Water (feed once if needed with ½‑strength grow) | ½–¾ every other watering | ||||||||
Switch from grow to bloom nutrients when you change from 18/6 to 12/12 (or within a week). Full‑strength feeds are for big, heavy‑feeding plants in active recirculating systems (e.g., NFT). In pots, it’s rarely necessary to exceed three‑quarters strength.
Most bottles list a “normal/half/full strength” dilution rate; some include a specific “seedling strength” too—use those as your product‑specific reference alongside the table above.
How to Create a Nutrient Solution
1) Calibrate and Prepare
Calibrate pH and CF/EC meters following manufacturer instructions. Accuracy here saves headaches later.
2) Take a Background Reading
Fill your tank with tap water that’s stood for 24 hours. Measure and note the background CF/EC and pH before you add anything.
3) Add Nutrients and Set Strength
Dose nutrients to the appropriate strength for your stage/system, mixing thoroughly between parts. Account for the background CF — additives can nudge readings up. If the solution is too strong, add more water.
4) Set pH
With the solution circulating in the system, check pH for a “real” reading. As a guide, aim around pH 6.3–6.6 for NFT, Flood & Drain, and DWC. If pH is high, add small drops of pH Down to correct.
Best Practice & Tips
- Keep nutrient temperature stable (roughly 18–21 °C) for root health and oxygen levels.
- Oxygenate tanks with air stones or circulation to keep solutions fresh.
- Record pH/CF and volumes for repeatable results.
- Refresh tanks regularly; top up with half‑strength between full changes.
