Your system holds plain water, every joint is dry and the film runs evenly in all channels. Now you turn that water into a nutrient solution. This lesson covers the two numbers you will manage for the life of the system — pH and EC — and the order of operations that keeps you out of trouble.
What the two numbers mean
EC (electrical conductivity) measures how much dissolved mineral salt is in the water, reported in mS/cm. It tells you how much food is present. It does not tell you which nutrients — a solution can read a perfect EC while being short of a specific element.
pH measures acidity. It governs availability — whether the plant can actually take up what is dissolved. Nutrients that are present but locked out by wrong pH may as well not be there. Iron is the classic casualty: above about pH 6.5 it precipitates out, and you get yellowing between the veins of new leaves in a tank that tests as fully fed.
EC is the size of the meal. pH decides whether the plant can eat it. You need both right, and pH is the one that goes wrong faster.
Target ranges for NFT
| Measure | Target | Acceptable |
|---|---|---|
| pH | 5.8 – 6.2 | 5.5 – 6.5 |
| EC — seedlings, first week | 0.8 – 1.2 mS/cm | Up to 1.4 |
| EC — lettuce and leafy greens | 1.2 – 1.8 mS/cm | 1.0 – 2.0 |
| EC — herbs (basil, mint) | 1.4 – 2.0 mS/cm | 1.2 – 2.2 |
| Solution temperature | 18 – 22 °C | Below 24 °C |
In hot weather, drop EC by around 20%. Plants transpire more and drink more water relative to the nutrient they need, so the same EC hits them harder. Running high EC through a heatwave is a reliable way to produce tip burn.
Mixing the first charge — in this order
Most hydroponic nutrients come as a two-part concentrate, A and B. They are supplied separately for a reason. Part A contains calcium; Part B contains sulphates and phosphates. Mixed together at full concentration they react and precipitate out as an insoluble white sludge — the nutrients are then permanently unavailable to your plants and the residue blocks your pump.
- Fill the reservoir with plain water first. Never add concentrate to an empty tank.
- Measure the starting water. Municipal water in much of South Africa already carries an EC of 0.2 – 0.4 mS/cm. That baseline counts toward your target, so record it.
- Add Part A. Stir thoroughly. Wait. Let it disperse completely before going near Part B.
- Add Part B. Stir thoroughly. Never pour A and B into the same measuring jug, and never add them to the tank simultaneously.
- Let it circulate for 15 minutes before measuring anything. An unmixed tank gives meaningless readings.
- Measure EC. Below target, add more of both parts in equal ratio. Above target, dilute with plain water.
- Measure and adjust pH last. Adding nutrient changes pH, so there is no point setting pH before EC is settled.
Adjusting pH without overshooting
pH adjusters are far stronger than people expect. The universal beginner error is a large dose, an overshoot, a correction in the other direction, another overshoot, and a solution that is now a chemistry experiment.
- Add pH Down or pH Up in very small increments — on a 100 litre reservoir, start with 2 ml.
- Circulate for 10 – 15 minutes, then re-measure. The reading immediately after dosing is not the settled value.
- Repeat until you are inside range. Approach the target from one side rather than bouncing across it.
- Wear eye protection. Concentrated pH adjusters are corrosive.
A newly mixed solution will drift for the first day or two as it equilibrates. Check it daily at first — this is normal and it settles.
Your meters
Your readings are only as good as your meters, and a pH pen that has drifted will confidently report a number that is simply wrong.
- Calibrate the pH pen against buffer solution — monthly at minimum, and always before commissioning a new system. Use fresh buffer; it degrades once opened.
- Store the pH probe wet, in storage solution. A probe stored dry is usually ruined, and this is the most common way people destroy an otherwise good meter.
- Rinse the probe in clean water before and after every use.
- EC meters need calibration far less often, but check yours annually against a known standard.
- Temperature affects both readings — a meter with automatic temperature compensation is worth the small extra cost.
Commissioning checklist
- Plain-water leak test passed (Part 3)
- Source water EC recorded
- Part A added, stirred, dispersed — then Part B
- Circulated 15 minutes before measuring
- EC set for the intended crop
- pH adjusted last, in small increments, to 5.8 – 6.2
- Solution temperature confirmed under 24 °C
- Film running evenly in every channel
- pH pen calibrated
Run the system on nutrient solution for 24 hours and re-check pH and EC before transplanting. Part 5 covers getting plants into the channels.
Basic Hydroponics Training — the full series
- Part 1 — NFT Hydroponics Explained: How the Nutrient Film Technique Works
- Part 2 — Planning Your NFT System: Space, Water, Power and Crop Choice
- Part 3 — Assembling a Vertical NFT System: Channels, Slope and Plumbing
- Part 4 — Commissioning Your NFT System: First Fill, Nutrients, pH and EC (you are here)
- Part 5 — Planting Out: From Seed to Channel
- Part 6 — Weekly Maintenance and Troubleshooting for NFT Systems
Own our wall-mounted system? Setting Up the Hydro Works Wall-Mounted NFT System gives you the build and commissioning steps for that specific unit.