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, hydroponic system, and reservoir size and gives you exact pH targets, seedling and mature EC, PPM on both meter scales, water and air temperature, light schedule, 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 22 hydroponic plants including lettuce, basil, cilantro, cherry 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. Your answer changes the feeding and top-off advice, because Kratky works on opposite rules to everything else.
- Enter your water volume in litres or gallons. The calculator works out exact doses in millilitres for your exact reservoir size.
- Mix, then measure. The doses are a starting point. Fill, add nutrients, stir, then check EC with a meter and adjust before you set pH. Always set pH last, because adding nutrients moves it.
❓ Common questions about hydroponic pH and nutrients
🧪 What is the ideal pH for hydroponic growing?
Almost every hydroponic herb and leafy green grows 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. Fruiting crops like cherry tomatoes and dwarf peppers prefer the narrower band of 5.8 to 6.5. There are two real exceptions worth memorising: cilantro wants 6.5 to 6.7, and watercress wants 6.5 to 7.0. Check pH every 2 to 3 days and adjust with pH Up or pH Down.
⚡ 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. Seedlings start at EC 1.0 for every crop except microgreens, which run 0.5 to 1.0. Mature EC depends heavily on the crop: lettuce sits at 1.0 to 1.4, basil at 1.8 to 2.2, and cherry tomatoes at 2.0 to 2.5. Feeding basil at lettuce strength is one of the most common reasons herbs stay small.
📊 What is the difference between EC and PPM?
EC and PPM measure the same thing but use different scales. On the 700 scale, PPM equals EC multiplied by 700, so EC 1.5 equals 1,050 PPM. On the 500 scale it equals EC multiplied by 500, so the same water reads 750 PPM. Always check which scale your meter uses, since a reading of 750 could mean you are perfectly fed or badly underfed depending on the device. EC is the more reliable standard because it does not vary by equipment. The calculator above shows both.
🚰 Can I use tap water for hydroponics?
Yes, most tap water works fine. Measure your starting EC before you add anything. If it reads above 0.4 mS/cm your water already carries dissolved minerals, so subtract that number from your target and mix less nutrient than the label says. Very hard water above 0.8 EC can cause lockout over time. Let water stand 24 hours to off-gas chlorine, or use a filter. Testing your tap water once tells you more than any general guidance can.
💊 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 nutrient systems 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 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, or it will precipitate out and do nothing.
🔄 How often should I change my hydroponic reservoir?
Do a full reservoir change every 2 weeks, for every crop. Between changes, top off daily with plain pH-adjusted water only, never with nutrient solution. Topping off with nutrients is exactly how salts accumulate, and it is one of the most common beginner mistakes. Kratky is the one exception, because you never refill a Kratky jar early. The widening air gap is what lets the upper roots breathe.
🌡️ What is the best water temperature for hydroponics?
65 to 72 degrees F (18 to 22 degrees C) at the root zone, for every crop. Water temperature is not crop-dependent the way air temperature is, which trips up a lot of people who assume tomatoes want warm water because they want a warm room. Above 72 F dissolved oxygen falls and root rot risk climbs fast, and that is the single most common cause of failure in a warm apartment. Never cool with ice cubes, since the swing shocks roots and the effect fades within an hour. Put a frozen bottle against the outside of the container instead.
🔍 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, so raise EC by 0.2 to 0.3. Brown leaf tips, crispy edges, and wilting despite wet roots means overfeeding, so lower EC by 0.2 to 0.4. Check pH before you change anything, though, because out-of-range pH produces the exact same symptoms even when EC reads correctly. A basic pH and EC meter set starts at $16.99 and covers everything you need.
🔒 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 though they are sitting right there in the water. Plants show deficiency symptoms despite a correct EC reading, which is why people keep adding more food and make it worse. Fix it by flushing the reservoir with plain pH-adjusted water, then refilling with fresh 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, tolerates a wider pH and EC range than most crops, and is ready in 4 to 5 weeks. It works in any system including a simple mason jar Kratky setup. Mint and basil are close behind. Cilantro looks like a beginner herb and gets recommended as one constantly, but it is not, since it needs its own pH of 6.5 to 6.7 and bolts faster than anything else on the shelf.