Seedlings: 0.5-0.8 EC (350-560 PPM). Vegetative: 1.0-1.6 EC (700-1120 PPM). Flowering/Fruiting: 1.6-2.4 EC (1120-1680 PPM). Adjust based on plant response.

Start seedlings at 0.5 EC and increase by 0.2 EC per week until reaching target stage EC
Lettuce and herbs prefer lower EC (0.8–1.2); tomatoes and peppers need higher EC (1.8–2.4)
If leaf tips burn (brown edges), reduce EC by 0.2–0.4 immediately
If EC rises between top-offs, plants are drinking more water than nutrients – dilute with plain water
If EC drops between top-offs, plants are consuming nutrients fast – top off with full-strength solution

Growth Stage	EC Range	PPM (700 scale)
Seedlings/Clones	0.5–0.8	350–560
Early Vegetative	0.8–1.2	560–840
Late Vegetative	1.2–1.6	840–1120
Flowering/Fruiting	1.6–2.4	1120–1680

How do I convert EC to PPM?

PPM = EC × 500 (Hanna scale) or EC × 700 (Truncheon scale). Most nutrient companies use the 700 scale. An EC of 2.0 equals 1400 PPM on the 700 scale.

Hanna/HM Digital meters use 500 scale: EC 2.0 = 1,000 PPM
Truncheon/BlueLab meters use 700 scale: EC 2.0 = 1,400 PPM
Check your meter manual to know which scale it uses – miscalibration is a common mistake
EC is the universal standard; PPM varies by manufacturer, so always note which scale you use
Calibrate your EC meter monthly with 1.413 EC (or 2.76 EC) reference solution for accurate readings

How often should I change hydroponic nutrients?

Change the reservoir every 1-2 weeks, or when nutrient levels become unbalanced. Top off with plain pH-adjusted water between changes to maintain concentration.

Small reservoirs (5–10 gal): change weekly since nutrient ratios shift faster
Larger reservoirs (20+ gal): change every 10–14 days for stable nutrient balance
Top off with pH-adjusted plain water (pH 5.8–6.0) when level drops 10–20%
Full reservoir dump costs $2–$5 in nutrients – cheaper than recovering stressed plants
Clean and sanitize the reservoir with hydrogen peroxide (3%) between nutrient changes

What pH is best for hydroponics?

Most plants prefer pH 5.5-6.5, with 5.8-6.2 being ideal. Some nutrients become unavailable outside this range. Check and adjust pH daily.

Target 5.8–6.0 for most leafy greens and herbs; 5.8–6.2 for tomatoes and peppers
pH above 6.5 locks out iron and manganese – causes yellowing between leaf veins
pH below 5.5 locks out calcium and magnesium – causes brown spots and stunted growth
Always add nutrients to water first, then adjust pH – nutrients shift pH significantly
Use phosphoric acid (pH Down) at 1–2 ml per gallon; potassium hydroxide (pH Up) at 0.5–1 ml per gallon

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Last Updated: Jul 2, 2026

This calculator is provided for informational and educational purposes only. Results are estimates and should not be considered professional financial, medical, legal, or other advice. Always consult a qualified professional before making important decisions. UseCalcPro is not responsible for any actions taken based on calculator results.

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