Estimative Index (EI) Dosing for Planted Tanks: Complete Method
Nutrient dosing can feel intimidating until you find a method that removes the guesswork. The Estimative Index (EI) dosing for planted tanks does exactly that — it ensures your aquatic plants never run short of any essential nutrient, allowing you to focus on lighting and CO2 instead. At Gensou Aquascaping Singapore, we have used EI dosing across countless client setups and our own display tanks, and it remains one of the most reliable fertilisation methods available to hobbyists.
What Is Estimative Index Dosing?
Developed by aquascaping researcher Tom Barr, the Estimative Index approach floods the water column with non-limiting levels of macronutrients (nitrogen, phosphorus, potassium) and micronutrients (iron, manganese, boron, and others). Rather than testing and fine-tuning individual nutrient levels, EI provides excess across the board and relies on a large weekly water change to reset concentrations and prevent accumulation. The philosophy is simple: if nothing is limiting, plants grow to their genetic potential.
Why EI Works So Well
Traditional dosing methods require frequent water testing and precise adjustments — a process that frustrates many hobbyists and often leads to deficiencies when one nutrient runs out before the next dose. EI sidesteps this entirely. By maintaining surplus levels of every nutrient, algae loses its competitive advantage (algae thrives when one nutrient is limiting while others accumulate), and plants remain healthy with vibrant colour and vigorous growth.
Standard EI Dosing Schedule
For a moderately planted high-tech tank (high light with pressurised CO2), the typical weekly schedule alternates between macronutrient and micronutrient days. Dose macros (potassium nitrate, potassium phosphate, potassium sulphate) on Monday, Wednesday, and Friday. Dose micros (a comprehensive trace mix containing iron and other elements) on Tuesday, Thursday, and Saturday. Rest on Sunday and perform a 50 percent water change to reset nutrient levels. Adjust quantities based on tank volume — standard EI targets roughly 20-30 ppm nitrate and 1-3 ppm phosphate over the week.
Dry Salts vs Liquid Fertilisers
EI dosing is most cost-effective using dry salts: potassium nitrate (KNO3), monopotassium phosphate (KH2PO4), and a trace element mix like CSM+B or Plantex. A year’s supply of dry salts for a 120-litre tank costs $15-30 SGD from local aquascaping suppliers or online via Shopee — a fraction of branded liquid fertiliser prices. Dissolve each salt separately in RO/DI water to create stock solutions stored in labelled bottles. A 500 ml solution of each lasts months.
The Weekly Water Change Reset
The 50 percent weekly water change is non-negotiable in EI dosing. It serves three purposes: removing excess nutrients before they reach problematic levels, replenishing CO2-depleted water, and eliminating organic waste. Singapore’s soft PUB tap water (treated with a quality dechlorinator) works well for planted freshwater tanks, unlike marine systems that require RO/DI water. This large water change also keeps TDS from creeping upward over time — a common issue in heavily dosed tanks without adequate resets.
Adjusting for Low-Tech Tanks
Tanks without CO2 injection and with moderate lighting need far less fertilisation. Reduce EI doses to one-quarter or one-third of the standard amounts, and decrease the water change to 30 percent weekly. Low-tech plants like Java fern, Anubias, Cryptocoryne, and mosses grow slowly enough that full EI dosing would simply feed algae. Observe plant health and adjust gradually — yellowing older leaves suggest nitrogen deficiency, while stunted new growth may indicate a micronutrient shortage.
Common Mistakes
Skipping the weekly water change is the most frequent error — nutrients accumulate, algae blooms follow, and hobbyists blame the method rather than their inconsistency. Using aquarium salt instead of proper dry fertiliser salts is another mistake we occasionally see. Finally, dosing EI levels without adequate CO2 and lighting creates a nutrient-rich environment that only algae can exploit. EI works best as part of a balanced system: strong light, consistent CO2, generous nutrients, and disciplined water changes.
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emilynakatani
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