Regime
Estimative Index (EI)
Philosophy
The Estimative Index (EI), developed by Tom Barr, is based on the theory of non-limiting abundance. The core philosophy dictates that by providing a constant excess of macro and micronutrients, nutrient deficiencies are completely eliminated as a cause of plant growth issues or failure. This removes the need for frequent, complex, and often inaccurate water testing to diagnose missing elements.
Rather than limiting nutrients to control algae—a traditional approach that often starves and weakens plants—EI focuses on maximizing plant growth as the primary natural defense against algae. The potential toxicity of nutrient accumulation is managed via a mandatory 50% weekly water change. This act of maintenance serves as a mathematical reset button, capping the maximum possible concentrations in the water column at exactly double the weekly dosage. Consequently, the hobbyist is freed to focus on the true drivers of plant health: light levels and stable carbon dioxide (CO2) delivery.
Recommended nutrient targets
| Parameter | mg/L |
|---|---|
| N (NO₃) | 20 |
| P (PO₄) | 2 |
| K | 30 |
| Fe | 0.5 |
| Mg | 5 |
| Ca | 20 |
| B | 0.02 |
| Mn | 0.5 |
| Zn | 0.03 |
| Cu | 0.01 |
| Mo | 0.003 |
Dosing frequency
3x/week macros (Mon-Wed-Fri), 3x/week micros (Tue-Thu-Sat)
Water change
50% weekly (mandatory)
CO2
Pressurized recommended (30 mg/L target)
Light
Medium-high (40-80+ PAR at substrate)
Pros
- Eliminates deficiency as a variable
- Rapid, lush growth
- Simple to calculate
- Well documented by the community
Cons
- Weekly water change mandatory
- High fertilizer consumption
- Algae risk if light/CO2 unbalanced
- Not suitable for low-tech
Common Errors
- •Skipping the mandatory 50% weekly water change, leading to toxic nutrient buildup.
- •Underdosing due to algae fears: EI fails if nutrients are not in 'non-limiting excess'.
Advanced Techniques
- •Reduce doses to 50-70% after the foreground carpet has closed to force plants to grow more compact and turn red (Nitrogen limitation).
Ideal for
High-tech planted tanks with pressurized CO2, intense light, and regular water changes. Ideal for aquascapers seeking maximum growth.
