Hydroponic pH and Nutrient Calculator
Getting your hydroponic pH and nutrient levels right is the single biggest factor in how well your plants grow. Too low on nutrients and your plants stay small and pale. Too high and you get salt burn, tip burn, and stunted roots.
This free calculator takes your crop type, hydroponic system, and reservoir size and gives you exact pH targets, EC ranges, and nutrient doses in millilitres. It works for Kratky jars, DWC buckets, NFT channels, and all-in-one kits like AeroGarden.
Step 1 of 3 – Choose your crop
What are you growing?
Your grow recipe
💧 Nutrient Doses for Your Reservoir
📋 How to use this hydroponic pH and nutrient calculator
- Choose your crop from 15 common hydroponic plants including lettuce, basil, tomatoes, microgreens, and more.
- Pick your system whether you are running a Kratky mason jar, a DWC bucket, an NFT channel, or an all-in-one kit like AeroGarden.
- Enter your water volume in litres or gallons. The calculator works out exact doses in millilitres for your exact reservoir size.
- Read your results and get your pH range, EC, PPM target, water temp, nutrient doses, a growing tip, and product recommendations in one place.
❓ Common questions about hydroponic pH and nutrients
🧪 What is the ideal pH for hydroponic growing?
Most hydroponic crops grow best between pH 5.5 and 6.5. Below 5.5, boron and manganese become toxic while calcium becomes unavailable. Above 7.0, iron and manganese lock out completely. Leafy greens like lettuce prefer 5.5 to 6.5, while fruiting crops like tomatoes do best at 5.8 to 6.3. Check your pH every few days and adjust with pH Up or pH Down solution.
⚡ What is EC and why does it matter?
EC stands for Electrical Conductivity and measures dissolved nutrients in your water in millisiemens per centimetre (mS/cm). Higher EC means stronger feeding. Low EC means underfed, pale plants that grow slowly. High EC causes tip burn, salt stress, and root damage. Most beginner crops run well at EC 0.8 to 1.6. Fruiting crops like tomatoes need EC 1.8 to 3.5 depending on growth stage.
📊 What is the difference between EC and PPM?
EC and PPM measure the same thing but use different scales. On the 700 scale (the most common globally), PPM equals EC multiplied by 700. For example, EC 1.5 equals 1,050 PPM. Some meters use the 500 scale, where EC 1.5 equals 750 PPM. Always check which scale your meter uses. EC is the more reliable standard because it does not vary by equipment.
🚰 Can I use tap water for hydroponics?
Yes, most tap water works fine. Check your starting EC first. If it is above 0.4 mS/cm your water already has dissolved minerals and you will need less nutrient solution. Very hard water above 0.8 EC can cause nutrient lockout over time. If in doubt, use a water filter or let water sit 24 hours to off-gas chlorine.
💊 Do I need CalMag in hydroponics?
Only if you are using reverse osmosis or very soft tap water with minimal dissolved minerals. You also need it if you see interveinal chlorosis (yellowing between leaf veins), weak stems, or tip burn on new growth. Standard dose is 1.25 ml per litre. Most complete A+B nutrient solutions already include calcium and magnesium, so check your base nutrients first. Short-cycle crops like lettuce and microgreens rarely need CalMag at all.
🧑 What is Silica and do I need it?
Silica is an optional supplement that strengthens plant cell walls, improving stem strength and disease resistance. It is most useful for fruiting crops like tomatoes and cucumbers under strong LED light, and for crops prone to powdery mildew. Standard dose is 0.1 to 0.25 ml per litre. For short-cycle crops like lettuce, microgreens, and wheatgrass you can skip it entirely. Always add silica to water first, before any other nutrients.
🔄 How often should I change my hydroponic reservoir?
For lettuce and herbs, change the full reservoir every 1 to 2 weeks. Top up with plain pH-adjusted water between changes as plants drink it down. For fruiting crops like tomatoes, a full change every 2 to 3 weeks works once your system is dialled in. Always adjust pH after adding fresh nutrients.
🌡️ What is the best water temperature for hydroponics?
Cool-season crops like lettuce, spinach, and microgreens prefer 18 to 22 degrees C (65 to 72 F). Warm-season crops like tomatoes and peppers grow best at 20 to 24 degrees C (68 to 75 F). Cucumbers prefer the warmest solution at 22 to 26 degrees C. Water above 24 degrees C for cool crops or 26 for warm crops holds less oxygen and encourages root rot.
🔍 How do I know if my plants are getting enough nutrients?
Healthy plants have deep green leaves, firm stems, and steady visible growth. Pale yellow-green leaves and slow growth means underfeeding – raise EC by 0.2 to 0.3. Brown leaf tips, crispy edges, and wilting despite wet roots means overfeeding – lower EC by 0.2 to 0.4. Use an EC meter to confirm rather than guessing. A basic pH and EC meter set starts at $16.99 on Amazon.
🔒 What is nutrient lockout and how do I fix it?
Nutrient lockout happens when pH drifts outside the 5.5 to 6.5 range, making nutrients chemically unavailable even if they are present in the water. Plants show deficiency symptoms despite correct EC. Fix it by doing a full reservoir flush with plain pH-adjusted water, then refill with fresh nutrient solution at the correct pH and EC.
🌱 What is the easiest crop to start with?
Lettuce is the best first crop for almost every beginner. It germinates in 2 to 3 days, grows fast, tolerates a wider pH and EC range than most crops, and is ready to harvest in 3 to 4 weeks. It works in any system including a simple mason jar Kratky setup. Use the calculator above to get the exact pH and EC targets for lettuce in your system.