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Estimative Index (EI) Fertilizer Tool | FishZone

Skip expensive commercial liquid supplements. Calculate precise DIY macro and micro dry fertilizer doses in exact parts per million (ppm) for your planted tank using the proven Estimative Index method. Enter your tank volume and target nutrient levels — get exact grams to measure.

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  • Reviewed by Experts
  • Updated May 2026
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Beginner

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Quick Answer

The Estimative Index (EI) method doses fertilizers generously throughout the week, then resets with a 50% water change every seven days. Standard weekly EI targets are 20 ppm Nitrate (NO3), 3 ppm Phosphate (PO4), 10–20 ppm Potassium (K), and 0.5 ppm Iron (Fe). The dose formula is: Mass in grams = (Target ppm × Tank volume in litres) ÷ (1000 × Elemental fraction of the compound). For a 100-litre tank targeting 20 ppm NO3 using KNO3 (61.33% NO3), you need 3.26 grams of KNO3 per dose. This calculator does all the maths for you — just enter your tank size and targets.

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How to Use This Calculator (Worked Example)

This tool requires 3 key inputs:

  1. System Volume (Gallons): Enter your specific value (e.g., from your tank's test kit or dimensions).
  2. Target Increase (ppm): Enter your specific value (e.g., from your tank's test kit or dimensions).
  3. Dry Compound Selection: Enter your specific value (e.g., from your tank's test kit or dimensions).

Example: If you input average baseline values, the calculator will immediately process the formula and return the recommended output and safety warnings above.

Method

This tool uses the visible inputs on the page and returns practical aquatics guidance for maintaining your tank.

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The Problem

Dry fertilizer dosing is dramatically cheaper and more precise than commercial liquid fertilizers, but the dose calculations — converting target ppm to grams of chemical compound per tank volume — require knowledge of elemental fractions for each compound and are error-prone to do manually. Errors in either direction cause deficiency symptoms, algae outbreaks, or in extreme cases harm to fish and shrimp. This calculator eliminates manual calculation errors and makes professional-grade EI dosing accessible to any hobbyist with a basic digital scale.

When to Use This Tool

Use this calculator when setting up an EI dosing programme for the first time to establish your weekly gram schedule for each compound. Use it when changing tank volume due to an upgrade or downgrade. Use it when adjusting targets in response to observed plant deficiencies or algae growth. Use it when switching between different chemical brands or grades that have different elemental fractions from standard values. Use it when adapting EI targets for a shrimp tank, low-tech setup, or heavily planted breeding tank with specific nutrient requirements.

Who is this for?

  • Intermediate and advanced planted aquarium hobbyists moving from commercial liquids to cost-effective dry fertilizers
  • Aquascapers managing high-tech CO2-injected planted tanks requiring precise nutrient control
  • Hobbyists troubleshooting persistent algae, deficiency symptoms, or stunted plant growth
  • Budget-conscious planted tank keepers looking to reduce ongoing fertilizer costs significantly
  • Shrimp breeders needing to calculate safe reduced-dose nutrient targets for sensitive Caridina and Neocaridina tanks
  • Hobbyists managing multiple planted tanks who need to scale doses accurately for different volumes
  • Planted tank beginners who want to understand the chemistry behind commercial fertilizer products

Dry fertilizers give planted aquarium hobbyists pharmaceutical-grade precision at a fraction of the cost of commercial liquid supplements. A bag of Potassium Nitrate that costs a few dollars online delivers months of macro dosing — the equivalent of hundreds of dollars in bottled plant food. But getting the dose right requires knowing exactly how many grams of each chemical raises your tank's nutrient level by a specific number of parts per million. That is precisely what this calculator solves.

Who Should Use This Calculator?

This tool is designed for planted aquarium hobbyists who have moved beyond commercial liquid fertilizers and want the precision, flexibility, and cost savings of dry chemical dosing. It is appropriate for intermediate hobbyists comfortable with basic aquarium chemistry and for advanced aquascapers managing demanding high-light, CO2-injected tanks where nutrient precision directly affects growth speed, plant colour, and algae control.

Beginners setting up their first planted tank may find commercial all-in-one liquid fertilizers easier as a starting point, but this calculator is a natural next step once you are ready to understand what goes into the water and why. It is also indispensable for hobbyists maintaining multiple tanks, shrimp breeders dialling in specific TDS targets, and anyone troubleshooting persistent algae or deficiency symptoms.

The Estimative Index Philosophy

Developed by Tom Barr in the early 2000s, the Estimative Index is built on a liberating principle: rather than trying to maintain perfect nutrient equilibrium through constant testing, simply provide more nutrients than the plants can possibly consume, then reset the system weekly. Plants possess a metabolic trait called luxury uptake, which allows them to absorb and store excess nutrients in their cellular vacuoles for use during high-demand growth phases — without suffering toxicity. Algae, by contrast, are opportunistic and respond more strongly to light and CO2 fluctuations than to nutrient excess. The EI method therefore controls algae not by starving the system, but by ensuring plants are always the dominant competitor.

The mandatory 50% weekly water change is not optional — it is the mathematical mechanism that prevents long-term accumulation of any element to toxic levels. Without it, ionic compounds (particularly potassium sulfate salts) can build to concentrations that stress fish and shrimp even if individual weekly doses are correct.

The Core Mathematical Model

The dose formula converts a target ppm increase into a mass of dry chemical compound to weigh out. It accounts for the fact that each compound contains only a fraction of the element you are targeting — the rest is the counter-ion or carrier molecule that contributes to TDS but not directly to the nutrient being dosed.

  • Potassium Nitrate (KNO3): 61.33% Nitrate (NO3-) by mass — the primary macro nitrogen source
  • Monopotassium Phosphate (KH2PO4): 69.79% Phosphate (PO43-) by mass — macro phosphorus and additional potassium
  • Potassium Sulfate (K2SO4): 44.87% Potassium (K+) by mass — pure potassium top-up without adding nitrogen or phosphorus
  • Magnesium Sulfate (MgSO4 · 7H2O, Epsom Salt): 9.86% Magnesium (Mg2+) by mass — macro secondary nutrient for chlorophyll synthesis
  • Chelated Iron (Fe-EDTA or Fe-DTPA): typically 7–13% elemental iron by mass — check your specific product label

The dosing formula is: Mass (grams) = [Target ppm increase × Tank volume (litres)] ÷ [1000 × Elemental fraction constant]. For stock solutions, this result is dissolved in a fixed volume of distilled water and dosed volumetrically with a syringe for daily convenience.

Standard EI Dosing Schedule

A typical EI week for a high-tech planted tank alternates macro and micro doses on separate days to prevent chemical interactions in the water column. Macros (KNO3, KH2PO4, K2SO4) are dosed on Monday, Wednesday, and Friday. Micros and trace elements (CSM+B or equivalent) are dosed on Tuesday, Thursday, and Saturday. Sunday is reserved for the 50% water change, which resets the nutrient slate. This separation prevents phosphate from precipitating iron out of solution before plants can absorb it, a common issue when both are dosed simultaneously.

EI for Low-Tech and Shrimp Tanks

Standard EI targets are designed for high-light, CO2-injected tanks with heavy plant mass. For low-tech tanks with ambient light and no CO2, reduce all macro targets by 50–75% — excess nutrients without the plant growth to consume them will directly feed algae. For dedicated shrimp tanks, particularly soft-water Caridina species, reduce targets further and monitor TDS closely. Full-strength EI dosing can push TDS up by 50–100 ppm per week, which stresses sensitive shrimp during moulting. A conservative starting point for shrimp-safe dosing is 5 ppm NO3, 0.5 ppm PO4, and 0.1 ppm Fe per dose.

When to Use This Calculator

Use it when transitioning from commercial liquid fertilizers to dry chemicals for the first time. Use it when setting up a new tank to calculate your weekly dose schedule before adding any plants. Use it when scaling doses for a tank of a new size, or when adjusting targets in response to observed deficiency symptoms, algae growth, or plant colour changes. Use it whenever you change the dry chemical compounds in your dosing kit, since different brands and grades carry different elemental fractions and require recalculation.

Reference Table

Static Planted Tank Dry Fertilizer Calculator: Estimative Index (EI) Dosing Reference

These baseline ratios and decision rules are included directly in the page so visitors can review core guidance before using the interactive calculator.

Scenario Baseline Rule Safety Note
Inputs used by this tool System Volume (Gallons), Target Increase (ppm), Dry Compound Selection The interactive calculator refines the result from these inputs.
Outputs generated Res mass, Res volume liters, Res fraction The static table gives baseline logic; final value depends on entered values.
Dosing MethodNutrient LevelWater Change RequirementTesting RequiredAlgae Control MechanismBest ForDifficulty
Estimative Index (EI)High — intentional saturation50% weekly — mandatoryNone required — maths-basedPlant dominance through nutrient saturation + CO2High-tech CO2-injected tanks with heavy plant massBeginner–Intermediate
PMDD (Poor Man's Dosing Dropper)Moderate — phosphate-limited25–30% weeklyRegular phosphate and nitrate testingPhosphate limitation starves algaeTanks without CO2 or with moderate plant densityIntermediate
ADA Lean Dosing (Substrate-based)Very low water column — rich substrateFrequent — 30% 2–3× weeklyExtensive — water column and substrate monitoringLean water column starves algae while substrate feeds rootsHigh-tech ADA-style Nature Aquarium setupsAdvanced
All-in-One Liquid FertilizersModerate — balanced but imprecise25% weekly typicalPeriodic testing recommendedBalanced approach — relies on correct doseBeginners and hobbyists preferring convenienceBeginner
Perpetual Preservation System (PPS-Pro)Low — daily micro-doses matching daily plant uptakeMinimal — 10–15% weeklyInitial calibration testing, then minimalNear-zero excess at all timesEstablished mature tanks with stable plant massAdvanced
Troubleshooting Guide
1 Plants are yellowing despite regular EI dosing

2 Algae outbreak despite following EI dosing schedule

3 Shrimp showing moulting problems or dying after dosing

4 Dry fertilizer powder not dissolving fully in stock solution

Glossary of Terms
Estimative Index (EI)
A planted tank fertilizer dosing method developed by Tom Barr that deliberately overdoses macronutrients and micronutrients throughout the week to ensure plants are never nutrient-limited, then resets accumulated concentrations with a 50% weekly water change.
Macronutrients (NPK)
The three primary nutrients required by aquatic plants in the largest quantities: Nitrogen (N), Phosphorus (P), and Potassium (K). In EI dosing, these are supplied by Potassium Nitrate (KNO3), Monopotassium Phosphate (KH2PO4), and Potassium Sulfate (K2SO4).
Micronutrients (Traces)
Elements required by aquatic plants in very small quantities but essential for metabolic function. These include Iron (Fe), Manganese (Mn), Zinc (Zn), Copper (Cu), Boron (B), and Molybdenum (Mo). Typically supplied as a chelated trace element blend such as Plantex CSM+B.
Elemental Fraction
The proportion by mass of the target nutrient element within a chemical compound. For example, KNO3 is 61.33% NO3 by mass. This constant is used in the EI dosing formula to calculate how many grams of compound are needed to deliver a specific ppm of the target element.
ppm (Parts Per Million)
The unit used to express dissolved nutrient concentrations in aquarium water. In freshwater aquariums, 1 ppm is equivalent to 1 milligram per litre (mg/L). Standard EI targets are expressed in ppm of each element.
Luxury Uptake
A metabolic trait of aquatic plants that allows them to absorb and store excess nutrients beyond their immediate requirements in cellular vacuoles. This buffering capacity is the biological justification for EI's deliberate overdosing approach — plants stockpile nutrients without harm and draw on reserves during peak growth phases.
Chelation
The chemical process of binding a metal ion (such as iron) to an organic molecule (the chelate) to keep it soluble in water. Unchelated iron precipitates rapidly as iron oxide (rust). Common chelating agents for aquarium use are EDTA (stable below pH 6.8) and DTPA (stable up to pH 7.5).
TDS (Total Dissolved Solids)
A measure of all dissolved ionic compounds in water, expressed in parts per million (ppm) or milligrams per litre. Dry fertilizer dosing increases TDS with each dose. EI's weekly water change resets TDS to acceptable levels. TDS is measured with an inexpensive conductivity or TDS pen meter.
Mobile Element
A plant nutrient that can be relocated from established older tissue to new growth when the plant experiences a deficiency. Nitrogen, Phosphorus, and Potassium are mobile — their deficiency symptoms appear on old leaves first as the plant cannibalises stored nutrients to protect new growth.
Immobile Element
A plant nutrient that, once incorporated into cellular structures, cannot be relocated. Iron, Calcium, Boron, and Manganese are immobile — their deficiency symptoms always appear on new growth first, since existing tissue retains its allocation even when supply is insufficient.
Potassium Nitrate (KNO3)
The primary nitrogen and potassium source in EI dry fertilizer dosing. Contains 61.33% Nitrate (NO3-) and 38.67% Potassium (K+) by mass. Food-grade and reagent-grade forms are both suitable for aquarium use.
Plantex CSM+B
A widely used chelated dry trace element blend for planted aquariums, containing a balanced profile of Iron, Manganese, Zinc, Copper, Boron, and Molybdenum. The B suffix indicates added Boron. It is the standard micronutrient recommendation for EI-dosed tanks and is available from most aquarium fertilizer vendors.
Interveinal Chlorosis
A distinctive yellowing pattern where the areas between leaf veins turn yellow while the veins themselves remain green. It is a classic visual indicator of Iron or Manganese deficiency and appears specifically on new growth due to the immobile nature of both elements.
Stock Solution
A concentrated liquid solution made by dissolving a precise mass of dry fertilizer powder in a measured volume of distilled water. Dosed daily with a graduated syringe, stock solutions allow convenient, accurate daily micro-dosing without weighing dry powder each time.
Scientific References
  1. The Estimative Index of Dosing — Original Method Paper
  2. Estimative Index: A New Approach to Plant Nutrition
  3. Nutrient Deficiency Identification in Aquatic Plants
  4. Chelated Iron Stability Constants and pH Dependence

Frequently Asked Questions

What is the Estimative Index (EI) method and how does it work?
The Estimative Index, developed by planted tank pioneer Tom Barr, is a fertilizer dosing philosophy for high-tech planted aquariums. Instead of trying to maintain precise nutrient equilibrium through constant water testing, EI deliberately overdoses macronutrients and micronutrients throughout the week, ensuring plants are never limited by nutrient availability. A mandatory 50% water change every seven days resets accumulated concentrations before they reach problematic levels. The system works because healthy, fast-growing plants are better competitors for nutrients than algae, and because plants can store excess nutrients in their cells without harm — a trait called luxury uptake.
How do I calculate how many grams of KNO3 I need for my planted tank?
Use the EI dosing formula: Mass in grams = (Target ppm × Tank volume in litres) ÷ (1000 × Elemental fraction). KNO3 is 61.33% Nitrate by mass, so the elemental fraction is 0.6133. To raise a 100-litre tank by 10 ppm Nitrate, the calculation is: (10 × 100) ÷ (1000 × 0.6133) = 1.63 grams of KNO3. For a standard EI target of 20 ppm NO3 per dose in the same 100-litre tank, you need 3.26 grams. The calculator above handles this automatically for any tank size and target level.
What are the standard EI target nutrient levels for a high-tech planted tank?
Standard weekly EI targets accumulate to roughly: 20–30 ppm Nitrate (NO3), 3–5 ppm Phosphate (PO4), 20–30 ppm Potassium (K), 5–10 ppm Magnesium (Mg), and 0.5–1.0 ppm Iron (Fe) as measured before the weekly water change. These are accumulation targets — the total built up across three macro doses per week — not single-dose targets. Individual doses are approximately one-third of the weekly total. After the 50% water change, concentrations are mathematically halved, establishing a repeating ceiling that cannot be permanently exceeded.
Which dry fertilizer chemicals do I need for the EI method?
A complete EI macro kit requires Potassium Nitrate (KNO3) for nitrogen and potassium, Monopotassium Phosphate (KH2PO4) for phosphorus and additional potassium, and Potassium Sulfate (K2SO4) to top up potassium without adding more nitrogen or phosphorus. For secondary macros, Magnesium Sulfate (MgSO4·7H2O, sold as Epsom Salt) is inexpensive and essential for magnesium. For micros and traces, a chelated trace element blend such as Plantex CSM+B (Compound Specific Micronutrient + Boron) is the standard recommendation, providing iron, manganese, zinc, copper, boron, and molybdenum in a single powder. All of these chemicals are available from aquarium specialty suppliers or agricultural and laboratory chemical vendors at a fraction of the cost of commercial liquid fertilizers.
What is the difference between EI, PMDD, and ADA lean dosing?
EI deliberately overdoses all nutrients and relies on weekly water changes as the reset mechanism. It is the most forgiving method for beginners transitioning to dry ferts and works best in high-light, high-CO2 tanks with heavy plant mass. PMDD (Poor Man's Dosing Dropper) intentionally limits phosphate to restrict algae growth, which can also starve modern high-demand plants and lead to deficiency issues in tanks with demanding species. ADA-style lean dosing relies heavily on a nutrient-rich aquasoil substrate to feed plants at the root zone while keeping the water column very lean — this suppresses algae and intensifies red pigmentation in some species through mild nitrogen stress, but it depends entirely on the substrate remaining active and becomes difficult to manage as the substrate depletes after 12–18 months.
Do I need to do a 50% water change every week if I use EI?
Yes — the weekly 50% water change is not optional in true EI. It is the mathematical mechanism that prevents long-term ionic accumulation. Without it, potassium and sulfate salts in particular can build to concentrations that affect fish health and alter water chemistry over months. Some experienced hobbyists adapt EI to a bi-weekly water change schedule by halving their weekly dose totals, but this requires more careful tracking. The beauty of weekly resets is that you do not need to test parameters between water changes — the maths guarantee that concentrations cannot exceed a defined ceiling.
How do I make a liquid stock solution from dry fertilizer powder?
Dissolve your calculated weekly or monthly dose of dry powder into a measured volume of distilled or RO water — typically 250 ml or 500 ml — in an amber glass or food-grade HDPE bottle. Label the bottle clearly with the compound name, concentration, and date. Dose daily with a graduated syringe. Keep stock solutions in the refrigerator to prevent mould growth, especially micronutrient solutions which are susceptible to bacterial contamination. Adding a small amount of Potassium Sorbate or a few ml of hydrogen peroxide (3%) as a preservative extends shelf life at room temperature. Do not mix macro and micro solutions into a single combined stock bottle — phosphate and iron will react and precipitate out of solution, rendering both ineffective.
Can I use the EI method in a low-tech planted tank without CO2 injection?
Yes, but standard EI targets need significant reduction. In a low-tech tank without pressurised CO2, plant growth rates are substantially lower and nutrient uptake is slower. Dosing at full EI targets in a low-tech tank will feed algae rather than plants. Start at 25–30% of standard EI targets and increase only if you observe deficiency symptoms. Many successful low-tech hobbyists dose just 5–8 ppm NO3 and 0.5–1 ppm PO4 per week and see excellent results. Liquid carbon products such as Seachem Excel or Aquario NEO Carbon can supplement CO2 in low-tech setups.
Is the EI method safe for shrimp tanks?
Full-strength EI is generally not recommended for sensitive shrimp species, particularly soft-water Caridina (Crystal Red, Taiwan Bee) shrimp. A full week of EI dosing can increase TDS by 50–100 ppm before the water change, which disrupts osmotic balance during moulting and can cause the fatal moulting failure known as the white ring of death. For Caridina tanks, reduce all targets by at least 50% and monitor TDS weekly with a conductivity meter. Neocaridina species (Cherry, Blue Dream, Snowball) are more tolerant of higher TDS but still benefit from moderated dosing. Use a fertilizer with chelated iron forms appropriate for your pH, and avoid high sulfate contributions from K2SO4 in shrimp breeding tanks.
What is chelated iron and which type should I use for my planted tank?
Chelated iron is elemental iron bound to an organic molecule (the chelate) that keeps it soluble in water rather than precipitating out as rust-like iron oxide. The two most common chelates used in aquariums are EDTA (ethylenediaminetetraacetic acid) and DTPA (diethylenetriaminepentaacetic acid). EDTA iron remains stable and plant-available in acidic water below pH 6.5 but degrades rapidly above that. DTPA iron remains stable up to approximately pH 7.5 and is the better choice for neutral or slightly alkaline planted tanks. For tanks above pH 7.5, HEEDTA or gluconate-chelated iron are more appropriate. Most commercial trace mixes like Plantex CSM+B use EDTA, making them best suited to acidic, soft-water planted tanks.
My plants have yellow leaves — is it a nutrient deficiency or something else?
Yellowing (chlorosis) has multiple possible causes and the pattern tells you a great deal about the source. Uniform yellowing of older leaves with green new growth suggests nitrogen deficiency — nitrogen is mobile and the plant pulls it from old leaves to protect new growth. Yellowing of new growth with green old leaves suggests iron or manganese deficiency — both are immobile elements that cannot be relocated from established tissue. Yellowing between the veins of new leaves specifically (interveinal chlorosis) is a classic iron deficiency signature. General yellowing across all leaf ages simultaneously often points to water chemistry issues — incorrect pH preventing nutrient uptake — rather than a true dosing deficiency. Always check pH and CO2 levels before increasing fertilizer doses.
How do I diagnose nutrient deficiencies by looking at my plants?
The key distinction is whether symptoms appear on old growth or new growth. Mobile elements — Nitrogen, Phosphorus, and Potassium — are relocated from old leaves to protect new growth when deficient. Nitrogen deficiency causes uniform pale yellowing starting on the oldest lower leaves. Phosphorus deficiency often presents as purple or reddish pigmentation on leaf undersides and stems. Potassium deficiency typically causes small necrotic pinholes or brown scorched edges on older leaves that progressively spread. Immobile elements — Iron, Calcium, Boron, and Manganese — cannot be relocated, so deficiencies appear exclusively on the newest growth. Severe iron deficiency produces completely white or translucent new leaves with green vein outlines. Calcium and boron deficiencies cause new leaf tips to emerge twisted, curled, or severely stunted.
Why are my plants growing well but I still have algae with EI dosing?
Algae in a well-fertilised EI tank almost always indicates a CO2 or light problem rather than a nutrient problem. The most common causes are: CO2 levels that are inconsistent or too low (target 25–30 ppm during the photoperiod, verified with a Drop Checker); excessive light intensity or photoperiod duration (reduce to 6–8 hours and add a mid-day siesta period); and nutrient imbalance where nitrogen is very low relative to phosphorus, encouraging algae. Green Spot Algae specifically indicates low phosphate. Black Beard Algae indicates CO2 fluctuations. Hair algae and Green Water indicate excess light relative to nutrient and CO2 levels. EI fertilizers remove nutrient limitation from the equation — if algae persists, investigate the other two pillars (CO2 and light).
What is the best ratio of Nitrate to Phosphate in a planted tank?
The widely referenced Redfield ratio adapted for aquatic plants suggests a NO3:PO4 ratio of approximately 10:1 by mass. Standard EI targets of 20 ppm NO3 and 2 ppm PO4 approximate this. In practice, planted tank hobbyists find that a ratio between 5:1 and 15:1 (NO3:PO4) supports healthy growth without algae dominance. Heavily planted tanks with fast-growing stem plants may tolerate and benefit from higher phosphate levels (3–5 ppm PO4) because phosphorus fuels rapid cell division. Tanks prone to algae outbreaks are often improved by increasing phosphate rather than reducing it — starving phosphate starves plants more than algae in most cases.
How do I know if my tap water already contains nutrients I should account for?
Request a water quality report from your municipal water supplier — most publish annual reports online. Key parameters to check are Nitrate (common in agricultural areas, sometimes exceeding 20 ppm from the tap), Phosphate (added by some water utilities as a corrosion inhibitor, typically 0.1–0.5 ppm), and Magnesium and Calcium (reflected in water hardness). If your tap water already contains significant Nitrate or Phosphate, reduce your EI doses by the equivalent amount to avoid overshooting targets. Hobbyists using RO or distilled water start from a blank slate and follow standard EI targets without adjustment.
Can EI dosing cause problems for fish in the tank?
When applied correctly with consistent weekly 50% water changes, EI is safe for the vast majority of freshwater fish. The nutrient concentrations involved are well within safe ranges for fish physiology. However, there are two important caveats. First, very high Nitrate accumulation — which can occur if water changes are skipped for multiple weeks — is harmful to fish above approximately 40–80 ppm depending on species sensitivity. Second, the ionic compounds introduced by dry fertilizers increase TDS and electrical conductivity, which affects sensitive soft-water species such as Discus, Altum Angelfish, and Caridina shrimp. For these species, reduce EI targets and maintain the weekly water change schedule rigorously.
What micro and trace elements do planted tanks need beyond NPK?
Beyond the primary macronutrients Nitrogen, Phosphorus, and Potassium, planted tanks require secondary macros — Magnesium (for chlorophyll molecule synthesis) and Calcium (for cell wall structure) — and a range of micronutrients in very small quantities: Iron (enzyme and chlorophyll production), Manganese (photosynthesis enzyme activation), Zinc (growth hormone regulation), Copper (electron transport in photosynthesis), Boron (cell wall formation and pollen development), and Molybdenum (nitrogen fixation enzymes). A quality chelated trace mix such as Plantex CSM+B provides all of these in appropriate ratios. Magnesium is often deficient in soft-water tanks and is easily supplemented with inexpensive Epsom Salt (MgSO4).
How do I transition from commercial liquid fertilizers to EI dry dosing?
Begin by identifying which liquid fertilizers you currently use and what nutrients they provide. Most liquid fertilizer labels list concentrations in ppm per dose or ml per litre. Calculate your current weekly nutrient inputs and use this calculator to determine the equivalent dry chemical doses for KNO3, KH2PO4, and a trace mix. Start at the lower end of EI targets (15 ppm NO3, 2 ppm PO4, 10 ppm K per week) rather than jumping to maximum targets immediately. Observe your plants and Drop Checker for two to three weeks before adjusting upward. The transition typically takes four to six weeks to fully dial in as you learn how your specific tank, plant mass, and light level consume nutrients.
Where do I buy dry fertilizer chemicals for planted aquariums?
The most cost-effective sources are aquarium specialty online retailers that sell pre-weighed hobby-grade dry fertilizer kits. These include vendors such as Aquarium Fertilizer (aquariumfertilizer.com), NilocG Aquatics, and GreenLeaf Aquariums in North America, and various Ebay or Amazon sellers offering reagent-grade KNO3, KH2PO4, and K2SO4. Agricultural fertilizer suppliers and laboratory chemical vendors also carry these compounds at larger quantities and lower unit costs, though purity grades vary. Epsom Salt (MgSO4) is available inexpensively at any pharmacy. Avoid industrial-grade chemicals that may contain anti-caking agents or heavy metal contaminants — look for reagent-grade or at minimum technical-grade purity.