Hydroponics Nutrient Calculator

Hydroponic nutrients must be precisely measured since plants have no soil buffer to compensate for errors. The two key measurements are EC (Electrical Conductivity) and PPM (Parts Per Million), which indicate the total dissolved nutrient concentration in the water.

EC and PPM Relationship: PPM (500 scale) = EC × 500 PPM (700 scale) = EC × 700

Note: There are two PPM scales in use. The 500 scale (TDS) is used in the United States. The 700 scale (CF) is used in Europe and Australia. Always check which scale your meter uses.

Optimal EC Ranges by Plant Type and Growth Stage:

Essential Nutrients (N-P-K and micronutrients):

Mixing Nutrient Solutions: Most commercial hydroponic nutrients come as 2-part or 3-part liquid concentrates. The standard mixing process:

1. Fill reservoir with water and check base water EC (tap water typically 0.2–0.5 EC)
2. Add Part A, mix thoroughly
3. Add Part B, mix thoroughly (never mix concentrates together undiluted)
4. Check EC and adjust: more nutrient raises it, more water lowers it
5. Check pH and adjust to 5.5–6.5 range

Dosage Formula: Concentrate (mL) = (Target EC − Base water EC) ÷ Concentrate strength × Reservoir volume (L)

Concentrate strength here means how much EC one millilitre per litre adds, and for ordinary two-part and three-part liquids that is about 0.3 mS/cm per mL/L. So raising a 100 litre reservoir by 1.0 EC takes roughly 330 mL of concentrate across all parts, or 3.3 mL per litre.

Be careful with this number, because it is easy to read off a label ten times too large. If a figure implies that one millilitre per litre gets you to EC 2.5, it is wrong: nobody feeds a hydroponic crop on a single millilitre per litre. An aggressive vegetative dose of General Hydroponics Flora is close to 8 mL per litre across the three bottles, and that lands near EC 2.0.

pH Management: Optimal pH: 5.5–6.5 for most hydroponic crops

Water Temperature: Nutrient solution should be maintained at 65–72°F (18–22°C). Cold water reduces nutrient uptake. Warm water above 75°F (24°C) reduces dissolved oxygen and encourages root disease (especially Pythium). Use a water chiller in warm climates.

Reservoir Management:

• Change nutrient solution completely every 7–14 days
• Top off with plain water between changes (evaporation concentrates nutrients)
• Monitor EC daily. If EC rises, plants are drinking more water than nutrients (add water); if EC drops, plants are feeding heavily (add nutrients)
• Keep the reservoir covered to block light and prevent algae growth

Starting Tip: When in doubt, start with lower nutrient concentration and increase gradually. It is much easier to correct a nutrient deficiency than nutrient burn (toxicity). Young plants and seedlings are especially sensitive to high EC.