Cultivation · Controlled Procedure
VC-SOP-0118 — Hydro-Loop Nutrient Dosing & pH Balance
The controlled procedure for dosing the closed hydroponic nutrient loops and correcting reservoir pH, holding each loop within its crop-class target band for electrical conductivity, pH, and nutrient ratio across the cultivation cycle.
Dose small, dose slow, verify before the next addition. The nominal substrate pH band is 5.8–6.2. Correct an elevated reservoir with the acidifying nutrient corrective (ANC-7) in increments no larger than 0.2 pH units per cycle, allowing one full loop turnover before re-reading. Never combine the acidifying corrective and the base corrective in the same dosing window — the closed loop will overshoot and stress the root mass.
1. Purpose
To define the controlled procedure for maintaining the closed hydroponic nutrient loops at the correct electrical conductivity (EC), pH, and macro/micronutrient ratio for each crop class. The objective is a stable root-zone chemistry that maximizes uptake while preventing the precipitation, lock-out, and osmotic stress that follow from over-dosing or out-of-band pH.
2. Scope
Applies to all closed recirculating nutrient loops serving greenhouse grid zones G-01 through G-24 and the Phyto-Synthesis feedstock loops. Covers automated injector dosing and manual corrective dosing of EC, pH, and nutrient stock. Reservoir thermal and humidity conditions are governed by VC-SOP-0212; overpressure and loop-rupture response by VC-SOP-0231. Excludes potable and sanitation water systems.
3. Definitions
| Term | Definition |
|---|---|
| EC | Electrical conductivity of the nutrient solution in mS/cm; a proxy for total dissolved nutrient strength. |
| Substrate pH | The root-zone pH measured at the substrate, distinct from raw reservoir pH; nominal band 5.8–6.2. |
| ANC-7 | Acidifying Nutrient Corrective, formula 7 — the standard corrective used to bring an elevated pH down while contributing nitrate. |
| BC-2 | Base Corrective, formula 2 — used to raise a depressed pH; never co-dosed with ANC-7. |
| Loop Turnover | One complete recirculation of the reservoir volume through the root zone and back; the minimum settle time before re-reading. |
| Drift Alarm | PhytoSense Mesh flag raised when EC or pH leaves the crop-class band for more than two consecutive reads. |
4. Responsibilities
| Role | Responsibility |
|---|---|
| Sr. Cultivar (Owner) | Approves corrective doses outside auto-bounds; sets crop-class target bands; owns this SOP. |
| Hydro Technician | Calibrates probes; prepares stock solutions; executes manual corrective dosing. |
| Cultivation Lead | Confirms crop-class assignment per zone and approves band changes for new specimens. |
| Climate Engineer | Consulted when reservoir temperature drives pH/EC drift per VC-SOP-0212. |
| CHLORA | Runs auto-dosing within bounds; logs every injection; raises drift alarms; locks out a second corrective until one loop turnover has elapsed. |
5. Equipment & Pre-Checks
- EC and pH probes calibrated within the last 24 h (two-point: pH 4.0 / 7.0)
- Reservoir temperature within 18–22 °C before any reading is trusted
- ANC-7 and BC-2 stock at labelled concentration, in date, segregated on the dosing rack
- Injector lines primed and free of crystallization; metering pumps verified to ±2%
- Loop turnover time known for the target reservoir volume
- Auto-dosing in known state (auto / manual) and the drift-alarm queue clear
6. Nutrient & pH Target Bands by Crop Class
Each loop is dosed to the band for its assigned crop class. Dose values are the standard per-turnover correction at full reservoir volume; halve for half-volume reservoirs.
| Crop Class | EC (mS/cm) | pH Band | Standard Dose / Turnover | Notes |
|---|---|---|---|---|
| Seedling / Propagation | 0.8–1.2 | 5.8–6.2 | ANC-7 4 mL/100 L | Lowest strength; pH most sensitive. |
| Leafy Vegetative | 1.4–1.8 | 5.8–6.2 | ANC-7 6 mL/100 L | High N uptake; watch EC creep. |
| Flowering Ornamental | 1.6–2.0 | 5.8–6.2 | ANC-7 6 mL/100 L | Shift to bloom stock at first flush. |
| Toxin-Bearing Cultivar | 1.8–2.4 | 5.8–6.2 | ANC-7 8 mL/100 L | Loop isolated; feedstock for Phyto-Synthesis. |
| Containment / GCL-3+ | 2.0–2.6 | 5.8–6.2 | By Sr. Cultivar order only | No auto-dosing; two-person manual dose. |
The pH band is uniform at 5.8–6.2 across all crop classes — only EC and nutrient strength vary by class. A reservoir reading above 6.2 is corrected down with ANC-7; below 5.8 with BC-2. Out-of-band by more than 0.4 pH units holds the loop and requires Sr. Cultivar sign-off before resuming auto-dosing.
7. Procedure
7.1 Probe Calibration & Baseline Read
- Two-point calibrate pH probes against fresh 4.0 and 7.0 buffers; single-point verify EC against 1.41 mS/cm standard.
- Confirm reservoir temperature is 18–22 °C; readings outside this are temperature-suspect and rejected.
- Record baseline EC, pH, and temperature for the loop against its crop-class band (Section 6).
7.2 Nutrient (EC) Dosing
- If EC is below band, dose nutrient stock to the class target; never raise EC by more than 0.4 mS/cm per turnover.
- If EC is above band, dilute with conditioned makeup water rather than draining; re-read after one turnover.
- Log the injected volume and the post-turnover EC against the band.
7.3 pH Correction
- For pH above 6.2, dose ANC-7 (the acidifying corrective) in increments ≤ 0.2 pH units, per the class dose in Section 6.
- For pH below 5.8, dose BC-2; never co-dose ANC-7 and BC-2 in the same window.
- Allow one full loop turnover before re-reading; confirm the substrate pH (not just reservoir pH) returns inside 5.8–6.2.
7.4 Drift Response & Hold
- On a drift alarm, verify the probe before adjusting chemistry — most drift alarms trace to a probe out of calibration or a temperature excursion.
- Genuine drift beyond 0.4 pH units or 0.6 mS/cm holds the loop and escalates to the Sr. Cultivar.
- Persistent drift with good probes is referred to the Climate Engineer for a reservoir thermal check per VC-SOP-0212.
7.5 Return to Auto-Dosing
- Confirm two consecutive in-band reads, one turnover apart, before handing the loop back to CHLORA auto-dosing.
- Sr. Cultivar signs off any loop that was held; the sign-off is attached to the dosing log.
- CHLORA resumes auto-dosing only within the class bounds; out-of-bound corrections remain manual.
7.6 Quality Checkpoints
- Probes calibrated within 24 h and temperature verified before any read
- pH held within 5.8–6.2; corrections capped at 0.2 units per turnover
- ANC-7 and BC-2 never co-dosed in one window
- EC inside the crop-class band after one turnover
- Held loops signed back to auto only after two in-band reads
8. Records
- Per-loop dosing log: baseline, injected volumes, post-turnover reads (MDF, retained 5 years)
- Probe calibration certificates and verification log
- Drift-alarm events and root-cause notes
- Sr. Cultivar sign-offs for held loops and out-of-band corrections
- Stock-solution batch and concentration records for ANC-7 / BC-2
9. References
- VC-SOP-0101 — Specimen Cultivation Cycle Management
- VC-SOP-0212 — Greenhouse Climate Control
- VC-SOP-0231 — Hydro-Loop Overpressure Response
- VC-SOP-0401 — Phyto-Synthesis Toxin Extraction
VC-SOP-0119— Nutrient Stock Preparation & Storage- Monitoring Systems · Operational Metrics
10. Revision History
| Rev | Date | Author | Summary |
|---|---|---|---|
| A | 2086-03-18 | Sr. Cultivar | Initial issue; EC and pH bands for three crop classes. |
| B | 2087-09-09 | Sr. Cultivar | ANC-7 acidifying corrective adopted; per-turnover dose caps introduced. |
| C | 2089-04-26 | Sr. Cultivar | Toxin-bearing and containment crop classes added; loop isolation rule. |
| D | 2090-08-12 | Sr. Cultivar | Substrate-pH (vs. reservoir) read-back mandated; drift-alarm probe-first rule. |
| E | 2091-02-14 | Sr. Cultivar | Co-dose lockout (ANC-7/BC-2) formalized; auto-dosing return criteria tightened. CBO approval. |