AnyponicsRunning it
Hydroponic nutrient schedule: EC and pH by growth stage
Feeding a hydroponic system is simpler than the wall of bottles at the grow shop suggests. There are really only two numbers to steer — EC and pH — and one step that most feeding charts leave out.
Start with EC, not with millilitres
Every nutrient bottle carries a feeding chart in millilitres per litre or gallon. Those charts are written for the manufacturer's own concentrate at a particular strength, and they assume your water starts at zero. Neither is usually true.
The number that actually transfers between brands, crops and setups is EC — electrical conductivity, in millisiemens per centimetre. It measures how much dissolved salt is in the solution, which is what the roots respond to. Mix to a target EC, then note how much of your particular bottle it took. That figure is yours from then on.
Target EC by crop
Leafy crops want a weak solution; fruiting crops want roughly twice as much. These are the ranges to aim for once plants are established.
| Crop | EC (mS/cm) | Notes |
|---|---|---|
| Lettuce and leafy greens | 0.8 – 1.4 | Bitter and prone to tipburn if pushed higher |
| Herbs (basil, mint) | 1.0 – 1.6 | Higher EC concentrates the oils and the flavour |
| Strawberries | 1.2 – 2.0 | Raise toward the top as fruit sets |
| Peppers | 1.8 – 2.8 | Steady feeding matters more than peak strength |
| Cucumbers | 1.8 – 2.5 | Heavy drinkers — EC climbs fast between top-ups |
| Tomatoes | 2.0 – 3.5 | The high end improves firmness and flavour |
| Microgreens | 0 – 0.8 | Usually plain water; the seed carries the energy |
Subtract your own water first
This is the step most feeding charts skip, and it is the most common cause of accidental overfeeding. Your source water already carries dissolved solids before you add anything:
- Reverse osmosis — about 0.0 mS/cm
- Rainwater — about 0.05 mS/cm
- Municipal tap — about 0.3 mS/cm, often higher in hard-water areas
- Well water — about 0.5 mS/cm and highly variable
If you are targeting 1.4 mS/cm on tap water that already reads 0.3, you only need to add 1.1 — not 1.4. Feed to the full figure and you land 20 per cent over target, every single mix.
A schedule by growth stage
Feed strength should ramp. Young roots burn easily; a plant carrying fruit is working far harder than a seedling.
| Stage | When | Strength | What to watch |
|---|---|---|---|
| Seedling | Weeks 1–2 | Roughly half the low end of the crop range | Browning leaf tips means it is already too strong |
| Vegetative | Weeks 3–6 | Around 60 per cent of the way up the range | EC climbing between top-ups means they are drinking faster than eating |
| Flower and fruit | Week 7 onward | Full strength, top of the range | Fruiting crops only — leafy greens stay at vegetative until harvest |
pH decides whether any of it is available
You can mix a perfect solution and still starve the plants. Nutrients only dissolve into a plant-available form across a narrow pH band, so pH is the gate in front of everything else.
- Hydroponics: pH 5.8 – 6.2. Above about 6.5, iron, manganese and phosphorus lock out first — you get deficiency symptoms in a reservoir that is technically full of food.
- Aquaponics: pH 6.8 – 7.0. Higher, because it is a compromise. Plants would prefer lower, but nitrifying bacteria stall below about 6.5 and the fish are unhappy at either extreme.
Correct pH before you correct anything else. A great many "deficiency" problems are a pH problem wearing a disguise.
Aquaponics is a different job entirely
If there are fish in the loop, do not dose a hydroponic base nutrient. The fish feed is the nutrient source: waste becomes ammonia, bacteria convert it to nitrate, and the plants take it up. Adding a hydroponic base on top pushes total dissolved salts past what the fish can tolerate.
What an aquaponic system genuinely runs short of is a shorter list:
- Chelated iron — 2–3 mg/L every few weeks. Iron deficiency is near-universal in aquaponics and shows first as yellowing between the veins of new leaves.
- Potassium — as potassium bicarbonate, which doubles as your pH buffer when the system drifts down.
- Calcium — as calcium hydroxide, alternated with the potassium so you are not always pushing the same ion.
Beyond those three, the lever is feed rate, not a bottle.
How often to check
Every other day is enough for an established system. For the first fortnight after starting up, check daily — a new system has small plants and a proportionally large reservoir, and it drifts.