The EI fertilizer dosing calculator calculates your weekly Estimative Index (EI) macro and micro fertilizer doses based on tank volume. EI deliberately overdoses nutrients to ensure no element limits plant growth, reset weekly with a 50% water change. Enter your tank size to get your complete EI schedule.
Tank Volume
Weekly EI Macro Totals
Dosing Schedule (per dose)
| Day | Fertilizer | Amount |
|---|
Important: 50% Water Change Weekly
EI requires a 50% water change every week to reset nutrient levels. Without the water change, nutrients accumulate to potentially harmful concentrations. Typically done on Saturday or Sunday before the new week's dosing begins.
How to Use the EI Fertilizer Method
The Estimative Index method eliminates nutrient deficiencies by dosing more than plants can consume, then resetting with weekly water changes. It's the most foolproof fertilization approach for high-tech planted tanks — if you have algae with EI, the cause is almost always light or CO2, not fertilizer balance.
Step 1: Calculate Your Doses
Enter your net tank volume (subtract substrate and decorations — typically subtract 10-20% from total volume). The calculator provides doses per 100L based on standard EI benchmarks: KNO3 13g, KH2PO4 2g, K2SO4 5g, trace mix 2g per 100L per week.
Step 2: Split Into 3 Macro Doses + 3 Micro Doses
Macros (KNO3, KH2PO4, K2SO4) are dosed Monday/Wednesday/Friday. Micros (trace mix) are dosed Tuesday/Thursday/Saturday. Never mix macros and micros — phosphate binds trace elements, making them unavailable to plants.
Step 3: Do the 50% Water Change
Every Sunday (or your chosen reset day), perform a 50% water change. This prevents nutrient accumulation and gives you a clean baseline for the next week. After the water change, you can optionally dose a half-dose of macros that same day.
Step 4: Adjust if Needed
If you see deficiency symptoms (yellowing leaves, holes in leaves), increase that nutrient by 25%. If you see algae outbreaks, first check CO2 and light consistency before cutting fertilizer — EI algae is almost never a fertilizer problem.
FAQ
What is the Estimative Index (EI) method?
The Estimative Index is a planted tank fertilization method developed by Tom Barr. It deliberately overdoses macro and micro nutrients to ensure no single nutrient is ever limiting. A 50% water change weekly resets the nutrient level, preventing toxic buildup while guaranteeing all plant needs are met.
How much KNO3 do I dose with EI?
Standard EI calls for approximately 13g of KNO3 per 100 liters per week, split into 3 doses. For a 60-liter tank, that's about 7.8g weekly or 2.6g per dose (Monday/Wednesday/Friday). Always weigh dry fertilizers rather than measuring by volume — density varies.
Do I need to do 50% water changes weekly?
Yes — the 50% weekly water change is essential to the EI method. Without it, nutrients accumulate to potentially harmful levels for fish and plants. The water change resets the nutrient baseline and removes any imbalances that have built up.
Can I use EI without CO2 injection?
EI works best with CO2 injection and high light. Without CO2, reduce doses to 50% and watch for algae. Low-tech tanks often do better with Perpetual Preservation System (PPS-Pro) or lean dosing methods rather than full EI.
Is this calculator free?
Yes, completely free with no signup required.
Does EI work for salt water tanks?
No. EI is designed specifically for freshwater planted tanks. Saltwater reef tanks use different fertilization approaches (two-part dosing, Zeovit, etc.).