Estimative Index Dosing Walkthrough Guide: Dry Salts Recipe

Tom Barr’s estimative index dosing system has been the workhorse method for high-tech planted tanks for nearly two decades, and despite a flood of all-in-one alternatives it remains the cheapest and most flexible way to feed a fast-growing scape. This walkthrough from Gensou Aquascaping at 5 Everton Park lays out the exact dry salt mix in grams per litre, the weekly schedule, and where Singapore tap water changes the maths compared to the original North American recipe.

The Core Idea Behind EI

Estimative Index assumes that water column nutrients are cheap and water changes are non-negotiable. Rather than test-and-adjust to a target, you dose a known weekly excess of nitrate, phosphate, potassium and traces, then a 50 per cent water change at week’s end resets everything. Plants take what they need, the residual goes down the drain, and you never deficit a fast grower mid-week. The trade-off is higher fertiliser usage — typically SGD 3-5 per month versus SGD 15-25 for branded all-in-ones.

Target Concentrations Per Week

Standard EI weekly targets are 20-30 ppm NO3, 3-6 ppm PO4, 30 ppm K, 0.5 ppm Fe, and trace micros. These are accumulated levels by water-change day, not single-dose values. Split the macros across three doses (typically Mon/Wed/Fri) and the micros across the alternate three days (Tue/Thu/Sat), with Sunday as the 50 per cent change-out. Pick up basic salts and a graduated cylinder from the fertilisers and additives section.

Dry Salt Recipe for a 200-Litre Tank

For a 200-litre net water volume, the standard EI weekly dose totals 7.5 g KNO3, 0.65 g KH2PO4, 5 g K2SO4 (optional if KNO3 already supplies enough K), and 0.5 g of a CSM+B-style trace mix. Split into three macro doses of 2.5 g KNO3 plus 0.22 g KH2PO4, dissolved in 500 ml of RO or boiled tap water in a labelled bottle. Trace mix dissolves separately at 0.17 g per micro day in 500 ml. A cheap 0.01 g jeweller’s scale costs SGD 15-20 on Shopee and is essential — kitchen scales cannot resolve KH2PO4 doses at this scale.

Scaling for Other Tank Sizes

Multiply or divide proportionally by net volume after substrate and hardscape displacement. A 60-litre nano needs 2.25 g KNO3 weekly (0.75 g per macro dose); a 350-litre showpiece needs 13 g KNO3. Always measure net volume rather than nameplate — a typical “60P” rimless holds about 55 litres of water once 4 cm of aquasoil is in. Underdosing because you forgot to subtract substrate is the most common EI failure pattern.

Mixing the Macro Stock Solution

Pre-mixed liquid stock is more practical than weighing salts daily. Combine all three weeks’ macros (22.5 g KNO3, 1.95 g KH2PO4) into 500 ml RO water, shake until fully dissolved (KNO3 takes 2-3 minutes), and dose 55 ml three times per week. Refrigerate the stock to prevent mould — Singapore ambient humidity will fuzz an unrefrigerated bottle within ten days. Trace stocks must be acidified with a pinch of citric acid or kept refrigerated to stop iron precipitation.

Singapore Tap Water Adjustments

PUB tap runs GH 2-4 and KH 1-2 — much softer than the GH 6-8 baseline most EI literature assumes. Plants need calcium and magnesium too, so add 4 g GH-booster (CaSO4 + MgSO4 in 3:1 ratio) per 100 litres at water change. Without this, you will see tip-curl on demanding plants like Rotala macrandra within a month even with macros and traces dosed perfectly. A GH and KH test kit verifies you hit GH 5-7 post-change.

Day-By-Day Schedule

Sunday: 50 per cent water change, GH-booster on the new water, no fert dose. Monday: macro dose 1, lights on schedule. Tuesday: trace dose 1. Wednesday: macro dose 2. Thursday: trace dose 2. Friday: macro dose 3. Saturday: trace dose 3. Lights run unchanged on a 7-9 hour photoperiod throughout. CO2 stays at 30 ppm for the full week — EI without stable CO2 produces algae faster than balance.

When EI Causes Algae

EI does not cause algae directly — unstable CO2 or excess light does, and the abundant nutrients then fuel the bloom that was always going to happen. If you see green dust algae or staghorn within two weeks of starting EI, audit CO2 distribution and photoperiod first. Halve the dose only if you have ruled out flow dead spots and confirmed 1.0+ pH drop from CO2.

Switching Off EI

Tanks that mature past the eighteen-month mark with slow-growing carpets and stems often grow faster than the keeper wants. Switch to a half-EI schedule (3 g KNO3 weekly for 200L) or migrate to lean dosing once the scape is filled in. The dosing pump category at Gensou makes the daily split-dose schedule painless once you commit to EI long-term.

Related Reading

• Lean Dosing Weekly Schedule Guide
• EI vs PPS-Pro Dosing Comparison Guide
• All-In-One Fertiliser vs Dry Salts Guide
• Planted Tank Water Change Schedule Guide
• Aquarium GH Booster Recipe Guide