EI dosing (the Estimative Index) is a method of fertilising high-tech planted tanks by deliberately adding more nutrients than the plants can use, then resetting levels with a large weekly water change, so plants are never short of anything and you never have to test the water. It is designed for CO2-injected, brightly-lit tanks with fast-growing plants. For most hobbyists, especially low-tech keepers, a simpler all-in-one fertilizer is easier and just as effective. This guide explains how EI dosing works, who it is for, a sample schedule, and how to decide between EI and all-in-one dosing.
EI has a reputation for being complicated, but the core idea is simple: provide nutrients in surplus, keep light and CO2 as the growth drivers, and use water changes to prevent build-up.
What is EI dosing?
Short answer: A dosing method that supplies non-limiting (surplus) nutrients to a high-tech tank, with a big weekly water change to reset levels.
The Estimative Index was developed for demanding, CO2-injected aquascapes where plants grow extremely fast and consume nutrients rapidly. Rather than testing and topping up precisely, EI “estimates” generously: you dose enough that no nutrient can ever run out, accept that there will be a surplus, and perform a large water change (typically 50%) once a week to bring everything back to a known low baseline. With light and CO2 as the only limiting factors, plants grow at their full potential.
How EI dosing works
EI splits the week into macronutrient days and micronutrient days. Macros (nitrogen, phosphorus, potassium) are dosed on some days; micros (iron and trace elements) on others. They are alternated because, in concentrated form, iron and phosphate can bind together and precipitate. At the end of the week, a big water change resets nutrient levels so they never accumulate to harmful highs. The cycle then repeats.
Who should use EI dosing?
- High-tech aquascapers running pressurised CO2 and strong lighting.
- Fast-growing plant collections, demanding stems, carpets, red plants.
- Hobbyists who do large weekly water changes anyway.
- People who want full control of each nutrient and do not want to test water.
EI is not ideal for low-tech tanks without CO2: dosing surplus nutrients into a slow-growing tank with modest light is a recipe for algae, because the plants cannot use the excess. Low-tech tanks do far better on light all-in-one dosing.
EI dosing vs all-in-one: which should you choose?
| Factor | EI dosing | All-in-one |
|---|---|---|
| Best for | High-tech CO2 tanks | Low-tech & most tanks |
| Complexity | Higher separate macros/micros, schedule | Low one bottle |
| Water changes | Large (50%) weekly, essential | Normal (25%) weekly |
| Control | Full control of each nutrient | Balanced, fixed ratio |
| Algae risk if mismatched | High in low-tech tanks | Low |
| Cost | Cheap per dose at scale (dry salts) | Great value for home tanks |
If you are not running CO2, choose an all-in-one like Sunken Garden Green, it gives excellent results with none of the complexity. Only move to EI when your tank is genuinely high-tech and you want maximum growth control.
A simpler middle ground
You do not have to choose between “full EI” and “bare minimum.” Many successful Indian aquascapers run a lean dosing approach a complete all-in-one dosed a little more heavily on a high-tech tank, plus a potassium or iron top-up if a specific deficiency appears. Products like Seachem Flourish Potassium let you add a single nutrient without committing to a full dry-salt EI regime. This gives much of EI’s flexibility with far less fuss.
For lean, flexible dosing
India-specific notes on EI
EI relies on large, regular water changes, easy enough where water is plentiful, but worth planning around in areas with water restrictions. Dry EI salts can be harder to source consistently in India, which is another reason many local hobbyists prefer a reliably-stocked all-in-one liquid. If you do run EI, your hard tap water already supplies calcium and magnesium, so you mainly dose NPK and iron.
Frequently asked questions
What does EI dosing mean?
Estimative Index a method of dosing surplus nutrients to a high-tech tank and resetting levels with a large weekly water change, so nutrients are never limiting.
Is EI dosing good for beginners?
Not usually. Beginners and low-tech tanks do better with a simple all-in-one. EI suits experienced high-tech aquascapers.
Do I need CO2 for EI dosing?
Effectively yes. EI is designed for CO2-injected, high-light tanks. Dosing surplus nutrients into a low-tech tank invites algae.
Why does EI use such big water changes?
The large weekly water change resets the surplus nutrients to a low baseline so they never build up to harmful levels.
Why are macros and micros dosed on separate days?
In concentrated form, iron and phosphate can bind and precipitate. Alternating days avoids this.
Is EI dosing better than all-in-one?
Not better just different. EI offers more control for high-tech tanks; all-in-one is simpler and ideal for most tanks.
Can I do EI with liquid fertilizers instead of dry salts?
Yes, you can run an EI-style schedule using separate liquid macro and micro fertilizers, though dry salts are cheaper at scale.
Will EI dosing cause algae?
In a properly balanced high-tech tank, no. In a low-tech tank with weak light and no CO2, the surplus nutrients can feed algae.
How much does EI dosing cost?
Dry EI salts are very cheap per dose, but require buying and mixing. For home tanks, an all-in-one is better value for the convenience.
Do I need to test water with EI?
No, the point of EI is to avoid testing by dosing surplus and resetting with water changes.
Can I run a lean version of EI?
Yes, lean dosing uses a complete fertilizer dosed moderately, with single-nutrient top-ups as needed. It is popular and low-fuss.
Is EI suitable for a low-tech tank?
No, low-tech tanks should use light all-in-one dosing, not EI surplus dosing.
What nutrients does EI dose?
Macros (nitrogen, phosphorus, potassium) on some days and micros (iron and trace elements) on others.
Is EI dosing worth it in India?
For dedicated high-tech aquascapers, yes. For most Indian hobbyists with low-tech or community tanks, a reliably-stocked all-in-one is the better choice.
Prefer simple over complex? Start with an all-in-one from the Sunken Garden range, or add single-nutrient control with options in the Aquarium Fertilizer collection. See also how to dose fertilizer and the complete fertilizer guide.
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