Hydroponic AB Nutrient EC / TDS Calculator
Hydroponic AB nutrient calculator: how many ml of stock A and B to reach your target EC, with TDS in ppm on the 500 and 700 scales, plus a top-up mode.
How to use
- Choose mixing a fresh tank or topping up an existing one.
- Enter your tank volume in litres. For top-up, also enter how much solution is left and its EC.
- Pick a crop preset to fill in a typical target EC, or type your own.
- Measure your plain water with an EC meter and enter it (0 if you don't know).
- Read your AB nutrient label and enter its dose — how many ml of A and of B per litre — and the EC that dose gives. The default (5 ml A + 5 ml B per litre ≈ EC 2.0) is only an example; brands differ.
- Read how many ml of A and B to add, the expected EC, and the TDS reading for both common meter scales.
How it's calculated
EC (electrical conductivity, mS/cm) rises roughly in proportion to the amount of nutrient in the water, so we scale the label dose:
- EC needed from nutrient = target EC − water EC
- Factor = EC needed ÷ label EC
- ml of A = label ml A per litre × factor × tank litres (same for B)
TDS meters show ppm by multiplying EC by a fixed factor. Meters differ, so both are shown:
- TDS (500 scale) = EC × 500
- TDS (700 scale) = EC × 700
Top-up mode assumes EC mixes in proportion to volume: the "EC × litres" still missing after you fill the tank with water is supplied by nutrient at the label rate.
Worked example
A 20 L tank of pak choy, target EC 1.8, tap water EC 0.1, label 5 ml A + 5 ml B per litre gives EC 2.0:
- EC needed = 1.8 − 0.1 = 1.7
- Factor = 1.7 ÷ 2.0 = 0.85 → 4.25 ml of each per litre
- A = 5 × 0.85 × 20 = 85 ml, B = 85 ml
- TDS = 1.8 × 500 = 900 ppm (500 scale) or 1.8 × 700 = 1,260 ppm (700 scale)
Top-up: 12 L is left at EC 1.9. Filling back to 20 L needs 8 L of water, and the calculator gives 31 ml each of A and B to bring the whole tank to EC 1.8.
Typical target EC
| Crop | Target EC (mS/cm) |
|---|---|
| Seedlings | 0.5–1.0 |
| Lettuce | 1.0–1.4 |
| Pak choy, choy sum, kailan | 1.5–2.0 |
| Kangkung, bayam | 1.4–2.0 |
| Herbs (basil, coriander, mint) | 1.0–1.6 |
| Tomato, chili, cucumber — fruiting | 2.0–3.0 |
These are typical starting ranges. In very hot weather many growers run leafy greens toward the lower end. Watch your plants: pale, slow growth suggests more nutrient; burnt leaf edges suggest less.
Tips
- Add A to the water and stir well, then add B. Never pour A and B concentrates into each other — they react and the nutrients become unavailable.
- Check EC after mixing and adjust; the calculation is a close estimate, not exact.
- Keep pH around 5.5–6.5.
- Replace the whole solution every 2–3 weeks so the nutrient balance does not drift.
- Keep tanks covered and dark to stop algae.
FAQ
My TDS meter reads differently from my friend's. Why? Meters use different conversion factors (often 500 or 700). Compare EC values instead, or check which scale your meter uses.
Why does my tap water have an EC? Tap water contains some dissolved minerals. Subtracting it stops you from overdosing nutrients.
Can I use this for Kratky? Yes. Mix the starting solution here. In Kratky the level drops as plants drink, so top up with half-strength solution or as your kit instructions say.
What if my water EC is higher than the target? The calculator will tell you. Use cleaner water, such as collected rain water, or mix it with your tap water.