How to EI Fertilization (Advanced Guide)
EI fertilization, also known as the Estimative Index method, is widely regarded as one of the most effective nutrient dosing strategies for planted aquariums. In this advanced guide from aquascaping.academy, you’ll learn how EI fertilization works, how to calculate precise dosing, tweak strategies for your tank, and troubleshoot common issues—empowering you to unlock explosive plant growth and incredible aquascapes.
What is EI Fertilization?
The EI fertilization method was popularized by Tom Barr as an easy, effective way to provide aquatic plants with all the macronutrients and micronutrients they need. Instead of attempting to keep precise target levels, EI relies on deliberate over-dosing, then performing regular water changes to reset nutrient concentrations. This results in:
- Eliminating nutrient deficiencies
- Consistent plant growth and coloration
- Algae minimized by healthy plant competition
This method is especially popular in high-tech, CO2-injected and well-lit aquariums but can be adapted for many tank setups.
The Core Principles of EI Dosing
At its core, EI fertilization means adding enough nutrients to ensure plants always have access to what they need, then removing the excess via weekly (usually 50%) water changes. The three primary macronutrients are:
- Nitrate (NO3)
- Phosphate (PO4)
- Potassium (K)
Trace elements (micronutrients) like iron, magnesium, and others are supplemented as well using a “trace mix” such as micronutrient aquarium fertilizers.
Standard EI Dosing Recommendations (per 40-50L aquarium):
- Nitrate (NO3): 20 ppm per week
- Phosphate (PO4): 2-3 ppm per week
- Potassium (K): 20–30 ppm per week
- Micronutrients: As recommended on product label, typically 0.5 ppm Fe per week
How to Calculate Your EI Doses
While commercial EI-ready products are available, seasoned aquascapers often mix their own solutions to save money and tweak ratios. Here’s how to create and dose your own EI fertilizers:
Step 1: Know Your Tank’s Net Volume
This is typically your tank’s physical volume minus substrate, hardscape, and displacement by décor. Accurate dosing starts with this measurement.
Step 2: Choose Your Salts and Supplies
- Potassium nitrate (KNO3) – nitrate + potassium source
- Potassium phosphate (KH2PO4) – phosphate + potassium
- Potassium sulfate (K2SO4) – extra potassium if needed
- Micronutrient mix (e.g., CSM+B or a reputable commercial trace blend)
Step 3: Mix Stock Solutions
Create stock solutions by dissolving salts in distilled water, which makes daily or weekly dosing easy and accurate. Consult a nutrient calculator or our aquascape calculator for precise measurements.
Step 4: Create a Dosing Schedule
The most common EI schedule looks like this:
- Day 1: Dose macros (KNO3 + KH2PO4 + K2SO4)
- Day 2: Dose traces (micronutrients/iron mix)
- Day 3: Dose macros
- Day 4: Dose traces
- Day 5: Dose macros
- Day 6: Dose traces
- Day 7: 50% water change and reset
This alternation prevents chemical interactions and ensures optimal uptake. Adjust doses based on plant growth, tank density, and observed results.
Fine-Tuning and Troubleshooting EI Fertilization
Advanced aquascapers will monitor their tanks closely and adjust EI dosing accordingly. Here are common adjustments and troubleshooting steps:
Signs of Nutrient Excess or Deficiency
- Yellowing leaves or slow growth: Possible nitrogen, potassium, or iron deficiency
- Stunted new growth or twisted leaves: Micronutrient deficiency
- Black or green spot algae: Potential phosphate imbalance or inconsistent CO2
- Green water or excessive algae: Reduce light intensity and ensure your water changes are consistent
Tweaking the EI Method for Your Aquarium
- Lower-tech/low-light tanks: Dose at half or quarter strength (“Lean EI”) to prevent excess buildup.
- Heavily planted/high-light/CO2-injected: Stick with full dosing, monitor and increase water changes if needed.
- Observe plant response and algae presence as key feedback.
Still seeing issues? Explore our algae control guide for more solutions.
Frequently Asked Questions About EI Fertilization
Do I have to dose every day?
No, but consistency is key. Some aquascapers use an “EI Lite” approach, dosing less frequently for slow-growth tanks.
Is EI safe for shrimp and sensitive fish?
When performed as described with regular water changes, EI fertilization is generally safe. Always acclimate sensitive species and observe closely.
Can I use liquid fertilizers instead of mixing dry salts?
Absolutely! Many brands offer pre-mixed EI formulas. Just be sure to dose according to both tank volume and plant density.
What if I miss a dose?
The occasional skipped dose won’t harm your plants, but keep your routine as consistent as possible for best results.
Get the Most From Your Aquascape With EI Fertilization
Mastering EI fertilization is an advanced but rewarding technique that empowers aquascapers to cultivate lush, healthy planted tanks with vibrant aquatic plants and minimal algae. With the right advanced aquascaping techniques, regular maintenance, and a dedication to observation, you can achieve truly spectacular underwater landscapes.
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