Counts carrier potassium
Potassium from KNO3 and KH2PO4 is calculated before any additional K2SO4 is added.
Planted aquarium fertilizing
EI dosing calculator
Calculate transparent dry-salt doses for the Estimative Index method, including the potassium already supplied by KNO₃ and KH₂PO₄.
Tank and method
Weekly nutrient targets
Standard EI (high-tech) preset · all values are fertilizer additions in ppm per week
These are weekly dose additions, not target test readings; existing nutrients are not subtracted. The trace calculation targets Fe in a dry powder only—do not use a liquid fertilizer analysis. Manganese, boron, zinc, copper, and molybdenum depend on the exact trace-mix recipe.
Fit check
Dry-salt plan
EI
See every contribution
The result separates weekly totals from per-dose masses and shows how much potassium is already supplied by the nitrate and phosphate salts.
Method references
EI target ranges vary between sources, so the preset remains editable. Review the method context before choosing a custom target.
Names the exact magnesium salt
The magnesium calculation uses MgSO4·7H2O, the heptahydrate commonly sold as Epsom salt, rather than an unspecified MgSO4 form.
Separates macros and micros
Weekly totals are divided into three macro and three micro doses on alternating days, followed by the weekly reset.
Estimative Index dosing guide
Calculate the salt mass and keep every nutrient contribution visible.
Estimative Index dosing supplies non-limiting nutrients during the week, then uses a large weekly water change to limit accumulation. There is no single universal EI recipe, so this calculator provides an editable high-tech starting preset and shows the chemistry behind every result.
Standard EI high-tech starting preset
These editable weekly targets reproduce a full alternating EI reference profile. Other established sources use different ranges, so treat the preset as a transparent baseline rather than a universal optimum.
| Nutrient | Weekly target | Primary source in calculator | Also supplied by |
|---|---|---|---|
| Nitrate (NO3) | 30 ppm | KNO3 | — |
| Phosphate (PO4) | 3 ppm | KH2PO4 | — |
| Potassium (K) | 40 ppm | K2SO4 as needed | KNO3 and KH2PO4 |
| Magnesium (Mg) | 3 ppm | MgSO4·7H2O | — |
| Iron (Fe) | 0.75 ppm | Trace mix by labeled Fe % | Product dependent |
How the EI salt calculation works
One ppm is one milligram per liter. Required compound mass equals target ppm multiplied by actual water volume, divided by 1,000 and by the nutrient's mass fraction in the compound. The result is a weekly mass in grams.
KNO3 is approximately 61.33 percent nitrate and 38.67 percent potassium by mass. KH2PO4 is approximately 69.79 percent phosphate and 28.73 percent potassium. K2SO4 is used only for the potassium still missing after those first two contributions are counted.
Why the hydrate form of magnesium sulfate matters
MgSO4·7H2O contains about 9.86 percent magnesium by mass. Anhydrous magnesium sulfate contains a different fraction, so using the wrong chemical form changes the dose substantially.
Confirm the exact formula and purity on the product label. The calculator assumes pure MgSO4·7H2O and does not compensate for fillers, moisture, or another hydrate.
A trace-mix iron percentage does not describe every trace element
The trace result uses the elemental Fe percentage printed on the product analysis. A seven percent Fe input means seven grams of elemental iron per 100 grams of trace mix.
That calculation targets iron only. Manganese, boron, zinc, copper, molybdenum, chelate type, and livestock suitability depend on the exact product formulation and cannot be inferred from Fe percentage alone.
When standard EI is and is not a good fit
Full EI is most closely associated with dense, fast-growing planted aquariums using strong light, stable injected CO2, regular trimming, and a consistent 50 percent or larger weekly water change.
A lightly planted, non-CO2, hardscape-heavy, or slow-growing aquarium usually has lower demand. Use custom lower targets or a leaner method rather than assuming the full preset is necessary.
Dry dosing and measurement precision
The calculator shows grams per dose without converting them to kitchen spoons. Powder density and particle size vary, while small fractional spoons are difficult to reproduce accurately.
Use a suitable precision scale. When a per-dose amount is below the scale's reliable resolution, prepare separate macro and micro stock solutions from verified weekly masses instead of rounding the dry powder by eye.
FAQ
EI Dosing Calculator FAQ
What is EI dosing?
Estimative Index is a planted-aquarium fertilizing approach that supplies nutrients in non-limiting amounts during the week and uses a large weekly water change to limit accumulation.
Why does KNO3 also add potassium?
KNO3 contains both nitrate and potassium. The calculator counts that potassium, plus potassium from KH2PO4, before calculating whether any K2SO4 is needed.
Can I use ordinary Epsom salt?
Only when the product is pure magnesium sulfate heptahydrate, MgSO4·7H2O, without fragrance or additives. Confirm the formula and purity on its label.
Why are macros and micros on different days?
Alternating the traditional macro and trace doses reduces the chance of iron and phosphate interacting before plants can use them and keeps the routine easy to audit.
Does EI require a weekly water change?
The classic EI routine uses a 50 percent or larger weekly water change as its reset. If that is not realistic, use a different or leaner dosing approach rather than the standard preset.
Is full EI suitable for a non-CO2 aquarium?
Usually not as a default. Non-CO2 and lightly planted aquariums have lower nutrient demand, so use conservative custom targets or a leaner method and observe plant response.
Related aquarium planning
Continue with the next aquarium decision.
Use the calculator result with logs, guides, and maintenance tools so one number becomes part of a repeatable aquarium care routine.
Aquarium Volume CalculatorEstimate actual water volume before calculating ppm-based fertilizer masses.Nitrate & Phosphate CalculatorReview measured NO3 and PO4 together after the dosing routine is established.CO2 CalculatorEstimate CO2 context from repeated KH and pH measurements in a planted aquarium.Planted Aquarium Dosing LogKeep fertilizer changes, water tests, plant response, and maintenance on one timeline.
Other tools
Try our other free tools!
Water chemistry
Nitrogen cycle helper
Interpret ammonia, nitrite, and nitrate with fish-in safety context and confirmation steps.
Cycle phaseFish-in warningsCheck cycle statusMaintenanceAquarium dosing calculator
Scale a product-label dose and convert mL, pumps, spoons, and density-aware grams.
Label scalingCustom pumpsCalculate doseEquipmentFilter flow & turnover calculator
Compare delivered flow with filter or display-circulation planning ranges.
Measured flowRated-flow estimateCalculate turnoverMeasurementAquarium unit converter
Convert aquarium volume, temperature, length, flow, GH, and alkalinity.
US and UK gallonsFlow and temperatureConvert unitsSaltwater chemistrySalinity converter
Convert specific gravity and practical salinity with temperature context.
SGPractical salinityConvert salinitySaltwater preparationSalt mix calculator
Scale product directions for a new batch or plan separately mixed correction water.
Product ratioReplacement batchCalculate salt mixBudgetingAquarium running cost calculator
Estimate electricity, replacement water, and recurring aquarium expenses.
kWhHeater duty cycleEstimate running costAll toolsBrowse all calculators
Explore aquarium planning tools for tank setup, stocking, aquascaping, nutrients, and planted tank care.
Tool directoryPlanning guidesBrowse toolsContinue in Aquarium Tracker
Turn the EI plan into a repeatable aquarium routine.
Keep fertilizer doses, water changes, NO3 and PO4 readings, plant photos, and adjustments together by aquarium.
Free to useBuilt for aquarium keepersSync across devices