EI Dosing for Planted Aquariums: The Estimative Index Explained

The Estimative Index (EI) is one of the most widely used fertilisation methods in the planted aquarium hobby. Developed by Tom Barr, it takes a refreshingly straightforward approach: provide plants with more nutrients than they can possibly use, and let CO2 be the only limiting factor. This EI dosing planted aquarium guide explains the philosophy, provides specific dosing schedules and helps you decide whether EI is the right approach for your Singapore tank.

What Is the Estimative Index?

The Estimative Index was developed by aquatic plant researcher Tom Barr in the early 2000s. It emerged from his observation that most algae problems in planted tanks are caused not by excess nutrients, but by nutrient deficiency and inconsistent CO2 — the opposite of what many hobbyists believed.

The core principle is simple: dose generous amounts of all essential nutrients so that plants always have access to everything they need. If all nutrients are available in excess, CO2 becomes the sole limiting factor for growth. A large weekly water change prevents nutrients from accumulating to problematic levels over time.

EI does not aim for precision. Unlike methods that test water and dose to exact target levels, EI “estimates” that providing excess of everything is sufficient. Hence the name: Estimative Index.

The EI Philosophy

Understanding the thinking behind EI helps you implement it correctly and troubleshoot effectively.

Key Principles

• Excess nutrients do not cause algae: Barr’s research showed that healthy, well-growing plants in a CO2-enriched environment outcompete algae regardless of nutrient levels. Algae problems arise when plants are stressed by deficiency, not abundance.
• CO2 is the primary limiting factor: In a high-tech tank, CO2 determines growth rate. As long as CO2 is adequate and consistent, excess nutrients cause no harm.
• No need for test kits: Because you deliberately dose excess, there is no point testing nitrate or phosphate levels. The answer is always “more than enough”. This simplifies maintenance enormously.
• Weekly reset: A 50% water change at the end of each week resets nutrient levels, preventing indefinite accumulation. This is the safety mechanism that makes the whole system work.

Chemicals Needed

EI dosing uses inexpensive dry fertiliser salts rather than commercial liquid formulations, making it very cost-effective in the long run.

These chemicals are available from aquarium suppliers, chemical suppliers and online sellers in Singapore. A single purchase of each salt typically lasts 6–12 months for a standard-sized tank, costing a fraction of what commercial liquid fertilisers would for the same period.

Preparing Solutions

Most hobbyists pre-dissolve the dry salts into stock solutions for easier daily dosing. Dissolve a measured quantity of each salt in distilled or RO water, then dose the appropriate volume of each solution on dosing days. Alternatively, dose the dry salts directly into the tank using a small measuring spoon.

Dosing Schedule

The classic EI schedule alternates macronutrients and micronutrients across the week, with a water change on day 7.

The alternating pattern prevents potential interactions between macro and micro elements (particularly iron and phosphate precipitating each other out of solution). While some hobbyists dose everything daily or on the same days without issues, the alternating schedule remains the standard recommendation.

Amounts by Tank Size

The following table provides standard EI dosing amounts per dosing day (three macro days and three micro days per week). These are the amounts for each individual dosing day, not the weekly total.

These amounts yield approximate weekly targets of 20–30 ppm NO3, 2–3 ppm PO4 and 0.5–1 ppm Fe. Exact precision is unnecessary — that is the entire point of EI. If you are within the right ballpark, the method works.

The Weekly Water Change

The 50% weekly water change is non-negotiable in the EI method. It serves as the system’s reset mechanism, preventing nutrients from accumulating week after week to extreme levels.

Why 50%?

Mathematically, a 50% water change each week ensures that even if plants consume nothing, nutrient levels never exceed approximately twice the weekly dose. In practice, plants consume a significant portion of what you add, so actual levels remain lower. The 50% change provides a generous safety margin.

Water Change Considerations in Singapore

Singapore’s PUB tap water must be treated for chloramine before addition to any aquarium. Use a conditioner like Seachem Prime that handles chloramine (not just chlorine). Temperature-match the replacement water to minimise stress on livestock, especially shrimp. In Singapore’s warm climate, tap water usually emerges at close to ambient temperature, simplifying this step.

The GH and KH of PUB tap water are relatively low. If you are keeping livestock that prefers harder water, consider adding a remineraliser after the water change to maintain consistent mineral levels.

Pros and Cons

Who Is EI Dosing For?

EI is best suited for high-tech planted tanks with pressurised CO2href=”/product-category/co2/”>CO2 injection, moderate to high lighting and growth-oriented plant selections. It excels in aquascapes dominated by demanding stem plants, carpeting species and red plants that require abundant nutrition.

EI Is a Good Fit If You:

• Run a CO2-injected planted tank.
• Are comfortable performing large weekly water changes.
• Want to stop worrying about nutrient deficiencies.
• Prefer a proven, simple system over constant testing and adjustment.
• Want to save money compared to commercial liquid fertilisers.

EI May Not Be Ideal If You:

• Run a low-tech or non-CO2 tank (excess nutrients without high CO2 can fuel algae).
• Keep sensitive shrimp that prefer minimal water-column nutrients.
• Cannot commit to 50% weekly water changes.
• Prefer a lean dosing philosophy where minimal nutrients are added. For an alternative approach, see our guide on lean dosing for planted aquariums.

Getting Started With EI in Singapore

1. Source your chemicals: KNO3, KH2PO4, MgSO4 and CSM+B / Plantex are available from local aquarium specialty shops and online. Gensou stocks individual salts and can advise on preparation.
2. Prepare stock solutions (optional): Dissolve measured amounts of each salt in RO or distilled water for easier daily dosing. Store in labelled bottles.
3. Ensure CO2 is sorted: EI assumes consistent, adequate CO2. Aim for a 1-point pH drop from degassed baseline, or approximately 30 ppm measured via the pH/KH method.
4. Begin dosing: Follow the schedule and amounts above, adjusted for your tank volume.
5. Perform a 50% water change weekly: Treat replacement water for chloramine. This is the cornerstone of EI.
6. Observe and adjust: If plants show deficiency symptoms despite EI dosing, the problem is almost certainly CO2 or light, not nutrients. Check CO2 levels first.

For a broader introduction to aquarium fertilisation, visit our liquid fertiliser aquarium guide.

Frequently Asked Questions

Will EI dosing cause algae?

Not if CO2 is adequate and consistent. Tom Barr’s central thesis is that excess nutrients in the presence of sufficient CO2 and healthy plant growth do not cause algae. Algae problems in EI-dosed tanks are almost always traceable to insufficient or fluctuating CO2, not the nutrient levels themselves.

Can I use EI in a low-tech tank without CO2?

It is not recommended. Without CO2 to drive plant growth, excess nutrients sit in the water column unused, which can promote algae. Low-tech tanks benefit from leaner dosing approaches where nutrients are matched more closely to actual plant uptake. See our lean dosing guide for an alternative.

Is EI safe for shrimp?

Neocaridina shrimp (cherry, orange, blue) tolerate EI dosing without issues, particularly with the weekly water change diluting everything. Sensitive Caridina species (Taiwan Bees, Crystal Red/Black) may benefit from a leaner approach, as they prefer very clean, low-TDS water. Many Caridina keepers use reduced EI amounts or switch to a lean dosing method entirely.

How much does EI dosing cost compared to commercial fertilisers?

Significantly less. A set of dry salts (KNO3, KH2PO4, MgSO4, CSM+B) costs roughly $20–$40 in Singapore and lasts 6–12 months for a standard-sized tank. Equivalent commercial liquid fertilisers for the same period would cost $60–$120 or more. The cost savings compound over time, making EI one of the most economical fertilisation methods available.

EI dosing has stood the test of time as a reliable, effective and economical way to fertilise high-tech planted aquariums. If you need help sourcing the chemicals or setting up an EI regimen for your specific tank, visit Gensou at 5 Everton Park or contact us — we have been helping Singapore aquascapers dial in their fertilisation for over 20 years.

Related Reading

• EI Dosing Complete Guide: Estimative Index for Planted Tanks
• How to Set Up Auto Dosing for Your Planted Aquarium
• Glutaraldehyde in Aquariums: Liquid Carbon and Algae Control
• Iron Dosing in Planted Aquariums: Red Plants Need It Most
• Lean Dosing Method for Planted Aquariums: Less Is More