Hydroponic Nutrient Management: pH, EC, PPM & Feeding Schedules
Table of Contents
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Macronutrients vs Micronutrients
Plants need two categories of nutrients:
Macronutrients (The Big Three)
Plants consume these in large quantities:
- Nitrogen (N): Drives vegetative growth, leaf development, stem strength. Nitrogen-heavy nutrients support leafy greens.
- Phosphorus (P): Essential for flowering, fruiting, and root development
- Potassium (K): Regulates water uptake, disease resistance, fruit quality
These three are abbreviated as NPK (Nitrogen-Phosphorus-Potassium). A nutrient label reads "10-5-7" meaning 10% nitrogen, 5% phosphorus, 7% potassium.
Secondary Nutrients
- Calcium (Ca): Prevents blossom-end rot in tomatoes/peppers
- Magnesium (Mg): Chlorophyll production (green color)
- Sulfur (S): Amino acid development
Micronutrients (Trace Elements)
Needed in tiny amounts: Iron (Fe), Manganese (Mn), Zinc (Zn), Copper (Cu), Boron (B), Molybdenum (Mo)
💡 Pro Tip: Most commercial hydroponic nutrient solutions already include all macros, secondaries, and micros in the correct ratios. You don't need to mix separately unless using advanced techniques. Browse complete nutrient solutions on Amazon.
Understanding pH Levels
pH measures acidity/alkalinity on a scale of 0-14. 7.0 is neutral. Below 7 is acidic, above 7 is alkaline.
Why pH Matters in Hydroponics
Plants can only absorb nutrients within certain pH ranges. If your pH is wrong, nutrient lockout occurs—nutrients are present but plants can't access them. This causes deficiencies even with proper nutrient dosing.
Optimal pH Ranges by Plant Type
| Plant Type | Optimal pH Range | Acceptable Range |
|---|---|---|
| Leafy Greens (Lettuce, Spinach) | 5.5-6.0 | 5.0-6.5 |
| Herbs (Basil, Mint, Cilantro) | 5.8-6.3 | 5.5-6.5 |
| Tomatoes | 5.8-6.2 | 5.5-6.5 |
| Peppers | 5.8-6.3 | 5.5-6.8 |
| Strawberries | 5.8-6.2 | 5.5-6.5 |
| Microgreens | 5.5-6.5 | 5.0-7.0 |
🎯 Beginner Rule
If you're growing multiple plants or unsure what to do, keep pH at 5.8-6.0. This range works for virtually all plants and gives good nutrient availability across the board.
How to Adjust pH
- pH Too High (above 6.5)? Use pH Down (phosphoric acid). Add a few drops, test, repeat. Most hydroponic systems ship with pH Down included. pH Down solutions on Amazon.
- pH Too Low (below 5.5)? Use pH Up (potassium hydroxide). Add drops, test, repeat. pH Up solutions on Amazon.
- Testing: Use a digital pH pen (accurate) or pH paper strips (cheaper, less accurate). Test after each change and wait 30 minutes for stability.
EC & PPM: Measuring Nutrient Strength
How much nutrient solution should you use? Two measurements help you dial this in:
EC (Electrical Conductivity)
- Unit: mS/cm (milliSiemens per centimeter)
- What it measures: How many dissolved mineral particles (nutrients) are in water
- Higher EC = More nutrients = More concentrated solution
- How it works: Minerals conduct electricity. More minerals = higher conductivity
PPM (Parts Per Million)
- Unit: ppm (milligrams of nutrients per liter)
- What it measures: Exact concentration of dissolved solids
- Conversion: EC × 500 = approximately PPM (varies by nutrients used)
Optimal EC/PPM Ranges by Plant Type
| Plant Type | EC Range | PPM Range (500x) | Growth Stage |
|---|---|---|---|
| Leafy Greens | 1.0-1.4 | 500-700 | All stages |
| Herbs (Veg) | 1.2-1.6 | 600-800 | Vegetative growth |
| Tomatoes (Veg) | 1.4-1.8 | 700-900 | Vegetative growth |
| Tomatoes (Fruit) | 1.8-2.2 | 900-1100 | Fruiting stage |
| Peppers (Fruit) | 1.8-2.1 | 900-1050 | Fruiting stage |
| Microgreens | 0.8-1.2 | 400-600 | All growth |
How to Measure EC/PPM
- Equipment: EC pen or TDS/EC meters on Amazon (digital, ~$30-50)
- Testing: Fill a small cup with reservoir water, dip meter, wait 10 seconds, read value
- Frequency: Test daily during first week, then 2-3x per week. Plants consume nutrients at different rates.
- Adjusting: If EC is too high, do partial water change. If too low, add more nutrient solution.
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Plant-Specific Feeding Schedules
Basil (Herbs)
- Optimal EC: 1.2-1.6 (600-800 ppm)
- pH: 5.8-6.2
- Nutrient Ratio (NPK): 7-9-5 (balanced, slight nitrogen boost)
- Schedule: Fill fresh nutrients week 1. Monitor daily. Plants consume nutrients fast. Maintain EC level, top off with water as plants drink. Full water change every 2-3 weeks.
- Light: 14-16 hours daily
- Expected Growth: Harvestable in 3-4 weeks from seedling
Lettuce (Leafy Greens)
- Optimal EC: 1.0-1.4 (500-700 ppm)
- pH: 5.5-6.0
- Nutrient Ratio (NPK): 10-5-7 or similar (more nitrogen for leaf growth)
- Schedule: Maintain consistent EC throughout growth. Partial water changes at 50% depletion. Full change every 3-4 weeks.
- Light: 14-16 hours daily
- Expected Growth: Harvestable in 4-5 weeks from seedling
Tomatoes (Fruiting Plant)
- Vegetative Phase (First 6 weeks):
- EC: 1.4-1.8 (700-900 ppm)
- NPK: 10-5-7 (nitrogen for growth)
- Flowering/Fruiting Phase (Weeks 7+):
- EC: 1.8-2.2 (900-1100 ppm)
- NPK: 5-10-10 (higher phosphorus/potassium for fruiting)
- pH: 5.8-6.2
- Schedule: As plants grow larger, nutrient consumption increases. Monitor EC closely. Expect 20-30% weekly decrease. Top off with water as needed. Full water change every 3-4 weeks.
- Light: 16-18 hours vegetative, 12 hours flowering
- Expected Growth: First flowers 6-8 weeks, ripe fruit 14-18 weeks
Nutrient Deficiency Chart
Plants show visible symptoms when nutrients are lacking. Here's how to identify and fix them:
Nitrogen (N) Deficiency
Symptoms: Yellowing of older (bottom) leaves, stunted growth, pale green color
Fix: Increase EC by 0.2-0.3, or do partial water change with fresh nutrients. Increase nitrogen-rich nutrient formula.
Phosphorus (P) Deficiency
Symptoms: Purple/reddish discoloration on stems and leaves, delayed flowering, weak roots
Fix: Switch to flowering nutrient formula (higher P). Increase EC. Ensure pH is 5.8-6.2 (P uptake optimized here).
Potassium (K) Deficiency
Symptoms: Leaf edges brown/burnt, weak stems, poor fruit quality
Fix: Increase EC by 0.3. Ensure pH 5.8-6.2. Full water change with potassium-rich formula.
Calcium (Ca) Deficiency
Symptoms: Blossom-end rot (black spots on bottom of tomato/pepper), new leaf damage
Fix: Increase calcium supplementation. Lower pH to 5.8 if high. Consistent watering prevents this.
Magnesium (Mg) Deficiency
Symptoms: Yellowing between leaf veins, veins stay green
Fix: Add magnesium sulfate (Epsom salt) at 65g per 10L water. Fold into your regular feeding.
Iron (Fe) Deficiency
Symptoms: Yellowing of new (top) leaves, pale color, stunted growth
Fix: Lower pH to 5.5-6.0 (improves Fe uptake). Use chelated iron supplement. Iron supplements on Amazon.
How to Mix & Change Nutrients
First-Time Nutrient Setup
- Fill reservoir with clean water (distilled or filtered preferred)
- Add nutrient solution per package instructions (usually 1 packet per 5-10 gallons)
- Add pH Up or Down to reach target pH (5.8-6.0)
- Wait 1 hour for full mixing, retest pH, adjust if needed
- Test EC/PPM, adjust if outside target range
- Now ready for plants
Water Changes (Recommended Every 3-4 Weeks)
- Drain old water completely from reservoir
- Rinse inside with distilled water
- Fill with fresh water
- Add fresh nutrient solution
- Adjust pH and EC as above
- Plant continues growth with fresh nutrients
⚠️ Why Change Water? Over time, plants absorb nutrients unevenly. Some accumulate, some deplete. pH drifts. Salts build up. A complete water change resets everything, preventing long-term problems.
Common Nutrient Mistakes
- Over-feeding (High EC): More nutrients doesn't mean faster growth. Too much causes nutrient burn (dark brown leaf tips), salt accumulation, and pH swings. Stick to recommended ranges.
- Ignoring pH: The #1 beginner mistake. Perfect nutrients with wrong pH = nutrient lockout. Plants starve despite adequate nutrients. Test pH twice weekly.
- Not Changing Water: Nutrients degrade, pH drifts, salts accumulate. Change water every 3-4 weeks minimum.
- Mixing Nutrients Incorrectly: Follow package instructions exactly. Some nutrients precipitate if added wrong (don't work).
- Using Tap Water: Tap water contains chlorine and minerals that affect EC. Use filtered or distilled water for more predictable results.
- Not Testing EC/PPM: Guessing nutrient strength leads to deficiencies or toxicity. Get an EC meter (~$30-50, essential tool).
Complete Your Nutrient Arsenal
Get the tools you need: nutrient solutions, pH testers, EC meters, and pH adjustment chemicals.
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