Hydroponic Reservoir Size Calculator
How many gallons of reservoir your hydroponic plants need, by crop and count.
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Nutrient Dose Calculator
How many mL of stock solution to dose a hydroponic reservoir up to your target ppm.
Nutrient Dose Calculator
Chlorova · updated for 2026
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The dose figures assume the ppm scale your meter reads on and a stock that mixes evenly, and they are a starting point to verify with your own meter, not a substitute for reading the reservoir. Real nutrients are sold at wildly different concentrations, two-part feeds must be added separately rather than premixed, and top-ups with plain water change the volume after mixing — so always measure the finished solution and adjust up in small steps rather than trusting the target blindly.
The nutrient dose calculator works out how much stock solution to add to a hydroponic reservoir to reach a target ppm, using the straight dilution math growers rely on. Choose a growth stage for a sensible working strength, enter the reservoir volume in liters and the concentration of your stock, and it returns the milliliters to dose, the per-liter rate, and the target ppm. Weaker seedling feeds and stronger flowering feeds come out of the same formula, so one tool covers a whole crop from clone to harvest without guessing at the mixing jug.
How to Dose a Reservoir
- Pick the growth stage that sets the working ppm target.
- Enter the total reservoir volume you are mixing, in liters.
- Enter the strength of your stock or mother solution in ppm.
- Read the milliliters of stock solution to add to the batch.
- Note the per-liter dose figure for topping the tank up later.
- Always add the stock to water, never water to concentrated stock.
- Stir the batch well, then check the reading with your own meter.
- Adjust in small steps until the meter settles at the target ppm.
How the Dose Is Worked Out
This is the standard dilution balance, stock strength times stock volume equals target strength times finished volume, rearranged to solve for the stock. Because a ppm is roughly a milligram per liter, the working dose in milliliters is the target ppm multiplied by the batch volume in milliliters, divided by the stock ppm — for a ten liter batch that is target × 10,000 ÷ stock. The per-liter figure is the same dose normalized to one liter, so you can scale a top-up without redoing the whole tank.
The growth-stage picker only sets the target ppm, and those defaults are the gentle middle of common ranges: about sixty for seedlings, one hundred and fifty for vegetative growth, and two hundred and forty once a plant flowers. Those are starting points, not rules, because crop, cultivar and lighting all shift the ideal strength. The meter is the final authority: mix to the calculated dose, measure the finished solution, and nudge up or down from there rather than assuming the arithmetic matches your particular bottle of nutrient.
Worked Example: A Ten Liter Veg Reservoir
- You are feeding a vegetative reservoir that holds about ten liters of freshly mixed water.
- The vegetative growth stage here sets a working target of about 150 ppm.
- Your concentrated stock or mother solution reads a strong 12,000 ppm.
- The dose works out to 150 × 10,000 ÷ 12,000 = 125 mL of stock.
- That is a per-liter rate of roughly 12.5 mL of stock per liter.
- Add that measured 125 mL of stock and stir the batch very thoroughly.
- Always measure the finished tank before you adjust the strength further.
- Top up lost volume with plain water, re-dosing at 12.5 mL per liter.
Example Doses for a 10 L Batch
Stock milliliters per ten liter reservoir at a 12,000 ppm stock, for each growth stage. Change the stock strength or batch volume in the calculator and the dose scales with them, since these are the same dilution formula evaluated at three targets.
| Growth stage | Target ppm | Stock to add (10 L) |
|---|---|---|
| Seedling | 60 | 50 mL |
| Vegetative | 150 | 125 mL |
| Flowering | 240 | 200 mL |
Key Terms
- ppm
- Parts per million, the meter's measure of dissolved nutrient; roughly a milligram per liter.
- Stock solution
- The concentrated mother liquid you dilute down to a working feed strength.
- Working strength
- The finished ppm in the reservoir after the stock is diluted into the batch.
- Two-part nutrient
- Separate concentrate bottles that must be dosed one at a time, never premixed neat.
- Top-up
- Refilling lost volume with plain water, then re-dosing the added water at the per-liter rate.
What This Means for a Steady Feed
- Add stock to water, never water to stock, because pouring water into a concentrated jug releases heat that can crash nutrients out before they reach the reservoir.
- The ppm you mix and the ppm the plant sees drift apart all week, since roots take up water and nutrients at very different rates between refreshes.
- Two-part and A/B feeds are dosed equally but separately, so stir one bottle in fully before the next, because mixing them neat crashes out insoluble salts.
- A weak solution you raise is far safer than a strong one you lower, since overshooting the target pulls water from tender roots and burns leaf tips.
- Every dose here leans on a ppm reading, so calibrate the meter monthly with a buffer tab, because a drifting meter makes the whole calculation confidently wrong.
Common Mistakes & Fixes
- Reading a bottle's dilution chart but not the concentration unit, then dosing from the wrong stock ppm.
- Mixing to a target the plant has outgrown, feeding a flowering crop at weak seedling strength all season.
- Pouring two-part concentrates together neat to save a step and knocking nutrients out of solution.
- Dosing once on day one and never re-checking as the reservoir drops and the strength concentrates.
- Trusting an uncalibrated meter and tuning the dose to fix a reading that was never real to begin with.
When to Use This (and When Not To)
Use it whenever you mix a hydroponic reservoir from a stock or concentrate and need the milliliters to hit a target ppm at a given volume. It handles dilution only — size the water volume itself with the hydroponic reservoir calculator, and translate an EC reading to ppm with the EC-to-PPM tool. For dry granular fertilizer going into soil at a weight rate rather than a liquid ppm, use the nitrogen calculator instead, since that math works in pounds and coverage, not milliliters and concentration.
Nutrient Dose Calculator: Frequently Asked Questions
How many mL of nutrient per liter for hydroponics?
It depends entirely on your stock concentration and target ppm, which is exactly why this calculator asks for both. A 12,000 ppm stock dosed to a 150 ppm vegetative target works out to about 12.5 mL per liter, but a different bottle changes the figure completely.
Is ppm the same as EC?
They measure the same dissolved-salt level on different scales, so a reading on one can be converted to the other. Note that ppm has two common conversions, so match the calculator and your meter to the same scale for consistent numbers.
Do I split the dose between two-part nutrients?
Yes. Add equal parts of each bottle separately, stirring one in fully before the next, and never mix the concentrates together while neat. Combined in strong form they react and fall out of solution, so the plant loses access to those nutrients.
What if I overshoot the target ppm?
Dilute it back down with plain water and re-measure rather than hoping the plants will drink it into range. A reservoir that reads far above target stresses roots and burns leaf tips, especially in seedlings and heat-stressed fruiting crops.
Should seedlings and flowering plants get the same dose?
No, and that is the reason the growth-stage picker exists here. Young plants want roughly a quarter of the strength of a flowering crop, so starting weak and building as the plant matures avoids the burn that a single strong feed causes.
Why does my reservoir ppm keep changing?
Because plants take up water and nutrients at different rates, so the balance drifts between refreshes even when nothing went wrong on your side. Topping up with plain water and re-dosing at the per-liter rate holds the strength steadier than one big mix.
Sources & Further Reading
- Nutrient Solution Management and ppm Dilution — Cornell Cooperative Extension controlled-environment agriculture program. Basis for the dilution model and stage-based target ppm defaults in this calculator.
- Conductivity, Mixing Order and Nutrient Availability — University of Florida IFAS Extension. Underpins the two-part dosing and add-stock-to-water cautions used here.
- Calibrating Refractometers and EC Meters for Hydroponics — Penn State Extension. Source of the meter-calibration and ppm-scale guidance on this page.
Chlorova Gardening Team
Builds, checks and documents every tool we publish
Chlorova editorial review
Checked against extension-service publications
Formula verified against published references · Updated
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