Buy a scale and a reliable pH/EC meter first. We dose every part by weight, and every problem we troubleshoot starts with feed and runoff pH and EC. Next comes a temperature/humidity reference and an infrared thermometer for leaf temperature, then a PAR meter when you start adjusting lights. Buy a controller or doser after you can measure what it's supposed to control.
What we use
| Tool | What we use | What it's for |
|---|---|---|
| Scale | Any accurate gram scale | Weighing powders. We dose by weight, never by teaspoon or scoop. |
| pH/EC meter | Bluelab Guardian monitors with replaceable probes | Feed, reservoir and runoff readings |
| Calibration supplies | Fresh pH buffers, EC reference solution, probe storage solution, cleaning supplies | Keeping the meter honest |
| Temperature/RH reference | Vaisala HM41 handheld | Checking the room and every other sensor |
| Remote sensors | Govee Wi-Fi hygrometers (H5179) | Budget option for trends while you're out of the room |
| Infrared thermometer | Fluke 64 | Leaf temperature for VPD |
| PAR meter | Apogee MQ-610 (ePAR, 400–750 nm) | Light at the canopy instead of guessing from wattage |
| Measuring containers | Graduated cup or bucket | Volume going in and runoff coming out |
The pH/EC meter
A cheaper meter isn't useless. It has to read reliably, and you need the calibration, storage and cleaning supplies to keep it that way. We liked the Guardians because you replace the pH probe instead of throwing out a whole pen. We've used American Marine Pinpoint probes on ours; match any replacement to your exact monitor model, not just the connector.
- Soak a new probe in storage solution, then calibrate with fresh buffers per the meter's instructions.
- If a probe won't hold calibration after cleaning, replace it. See why your pH meter keeps drifting.
- One meter can do the reservoir and runoff. Rinse the probes between samples.
- Read EC if your meter has it. If you use ppm, know your scale: our numbers use the 500 scale, so 2.2 EC is 1,100 ppm on 500 and 1,540 ppm on 700.
Check sensors against each other
Put the controller sensor and your reference side by side in the same shaded spot and let both settle before comparing. Apply an offset only if they still disagree there. If they agree side by side but read differently across the room, look at placement and airflow. A temperature/RH reference doesn't check a CO₂ sensor.
Most controllers assume a leaf-temperature offset instead of measuring it, which is why they often disagree with our VPD calculator. Use your measured air temperature, RH and leaf temperature in the calculator. On a light mover, measure through the whole cycle; the peak reading overstates what the plant gets all day.
Measure where it matters: at the canopy, at the dripper, and on a problem pot next to a healthy one. For remote monitoring setups, see how we use Govee sensors.
What can wait
On a big reservoir, continuous monitoring and a pH doser can save a lot of work. We've used Bluelab pH dosers, but a pH doser only adjusts pH; it doesn't replace the nutrient injectors. Build automation once your basic readings are dependable. See building a reliable automated irrigation system.
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