Find out exactly how much nutrient solution to add — or how much water to dilute with — based on your reservoir size and your crop's target EC.
1 What are you growing?
Select your crop to auto-fill the recommended target EC. You can adjust the number in Step 3 at any time.
2 Your reservoir
Enter the total volume in litres and your current EC reading. Fresh tap water in northern Europe is typically 0.2–0.5 mS/cm.
litres
mS/cm
No EC meter? Tap water in Estonia and northern Europe reads roughly 0.2–0.5 mS/cm. RO or filtered water starts near 0.0. For accurate results, an EC meter is worth investing in — see testers & meters at indoorgarden.ee.
3 Target EC
Auto-filled from your crop selection. Beginners: start at the midpoint and increase gradually over 1–2 weeks.
mS/cm
4 Nutrient product
Select your product. The three Shop products use dosing figures verified from their product pages. For anything else, pick from the dropdown or enter your own EC contribution value.
mS/cm
Check your product's technical data sheet (TDS). Most liquid nutrients add 0.15–0.35 mS/cm per ml per litre. Organic formulas (fish emulsions, BioBizz) tend to sit at the lower end.
Masterblend is a dry powder. This calculator works with liquid nutrient concentrates. For Masterblend, weigh your dose on a scale (standard recipe: 6 g per litre), dissolve in warm water, then use your EC meter to verify the result. Typical EC at full dose: 2.0–2.5 mS/cm.
1 Current reservoir
Enter the total volume of your reservoir and the EC you're reading right now.
litres
mS/cm
2 Target EC
The EC level you're aiming for. Switch to Raise EC and select your crop for recommended ranges by plant type.
mS/cm
Use low-EC water when diluting. Tap water already contains dissolved minerals (EC 0.2–0.5 mS/cm) — it dilutes less than pure water. RO or filtered water near 0.0 mS/cm gives the most predictable results. Formula used: C₁V₁ = C₂V₂.
EC and pH work together. Even when nutrient levels are correct, plants can't absorb them if pH is outside a narrow window. Always adjust EC first — then check pH, because adding nutrients changes the pH of your water.
Hydroponic pH scale — nutrient availability
4.5
5.0
5.3
5.5 – 6.5 ideal
6.8
7.0
7.5
Too acidicGood zoneToo alkaline
pH 5.5–6.5 — Ideal for hydroponics
All major nutrients are fully available to roots. Aim for around 6.0 as your daily target — it gives the most balanced uptake across all nutrient types. Some natural drift between checks is normal and does not need immediate action unless it crosses outside 5.5–6.5.
pH below 5.5 — Too acidic
Calcium and magnesium availability drops sharply, even when they're present in solution. Add pH Up (potassium hydroxide) in 0.5 ml increments. Stir thoroughly, wait 2 minutes, re-test. Never add large amounts at once.
pH above 6.5 — Too alkaline
Iron, manganese, and zinc become unavailable. Add pH Down (phosphoric or citric acid) in 0.5 ml increments. Stir well and wait 2 minutes before re-testing — pH changes are not instant in solution.
Good habits
Always mix nutrients into water first, then adjust pH. Adding nutrients changes the water pH, so doing it in reverse wastes pH solution.
Check pH every 2–3 days in the first week of a fresh reservoir. After that, weekly is usually fine for established plants.
A slow upward drift between checks is normal — plants consume some nutrients faster than others. A sudden large shift can signal a root health problem.
Smart garden pods (Botanium, LetPot) buffer pH automatically — no pH testing needed for pod-based systems.
Calibrate your pH meter every 1–2 months using calibration solution at pH 4.0 and 7.0. An uncalibrated meter is the most common cause of nutrient problems that beginners struggle to diagnose.