Aquarium Fertilizer Dosing: All-in-One vs Estimative Index for Planted Tanks

Plants need light, CO2, and seventeen essential nutrients to grow. Light comes from the LED, CO2 from injection or atmospheric equilibrium, and the nutrients come from fertilizer. A planted aquarium that grows poorly almost always has one of those three undersupplied, and in tanks with the light and CO2 dialed in correctly the bottleneck is fertilizer. This guide covers the two main dosing approaches (all-in-one liquid and Estimative Index), the macronutrient ratios that drive plant growth, the deficiency symptoms that tell you what is missing, and the dosing schedules for low-tech and high-tech tanks.

The seventeen essential nutrients

Plants need three macronutrients in large amounts: nitrogen (N), phosphorus (P), and potassium (K). They need four secondary nutrients in moderate amounts: calcium, magnesium, sulfur, and iron. And they need a dozen micronutrients in trace amounts: manganese, zinc, boron, copper, molybdenum, chlorine, nickel, sodium, and a few others.

In a planted aquarium:

• Nitrogen: comes from fish waste (ammonia, nitrate) and from KNO3 dosing. A stocked tank usually has plenty.
• Phosphorus: comes from fish food and from KH2PO4 dosing. Lightly stocked tanks often run short.
• Potassium: not produced by fish waste. Always needs supplementation.
• Iron: not present in tap water in plant-available form. Always needs supplementation.
• Trace elements: present in tap water in tiny amounts, almost always needs supplementation.

Method 1: All-in-One Liquid Dosing

The simplest approach. One bottle contains N, P, K, iron, and traces in a pre-mixed ratio. Dose 1 to 5 ml per 10 gallons once or twice a week, water change weekly, done.

Common all-in-one fertilizers in 2026:

• Easy Green (Aquarium Co-Op): 1 pump per 10 gallons weekly, the most popular all-in-one for low-tech and medium-tech tanks
• Seachem Flourish: a trace-heavy formula, dose 1 capful per 60 gallons twice a week
• Thrive (NilocG Aquatics): comes in three formulas (Thrive Low Tech, Thrive, Thrive+) calibrated for different tank intensities
• Tropica Specialised Nutrition and Tropica Premium: the European standards, lower N and P than US formulas to suit European tap water which is harder

All-in-one works well for:

• Low-tech tanks (no CO2)
• Medium-tech tanks (low CO2, 30 to 50 PAR lighting)
• Mixed planted tanks that do not lean heavily on one plant type
• Beginners who do not want to mix individual fertilizers

The downside: the ratio is fixed. If your tank runs low on phosphate but high on nitrate (a heavily stocked tank), an all-in-one will keep adding nitrate while still under-dosing phosphate. For most tanks this does not matter, but for optimized high-tech setups it limits results.

Method 2: Estimative Index (EI)

Estimative Index is a high-tech dosing method developed by Tom Barr. You dose individual dry fertilizers in heavy doses 3 to 4 times a week, with the assumption that any excess is removed by the weekly 50 percent water change.

A standard EI dose for a 40 gallon tank:

• KNO3 (potassium nitrate): 1/2 teaspoon, 3 times a week, delivers nitrogen and potassium
• KH2PO4 (monopotassium phosphate): 1/8 teaspoon, 3 times a week, delivers phosphorus and potassium
• K2SO4 (potassium sulfate): 1/4 teaspoon, twice a week, delivers extra potassium
• CSM+B (chelated trace mix): 1/4 teaspoon, 3 times a week, delivers iron and trace
• Weekly water change: 50 percent, resets the system

The target after a week of EI dosing:

• Nitrate: 10 to 20 ppm
• Phosphate: 1 to 2 ppm
• Potassium: 20 to 30 ppm
• Iron: 0.1 to 0.2 ppm

EI is the right choice for high-tech CO2 tanks with red stems, carpet plants, and demanding aquascapes. It is overkill for low-tech and mid-tech setups.

Method 3: PPS-Pro (Perpetual Preservation System)

A middle ground between all-in-one and EI. PPS-Pro doses smaller daily amounts of individual fertilizers to keep nutrient levels steady without the weekly reset. Suitable for keepers who do not want to do 50 percent weekly water changes.

The daily PPS-Pro dose for a 40 gallon: 1/16 teaspoon KNO3, a pinch of KH2PO4, a pinch of K2SO4, and a pinch of trace mix. Lower water changes (20 to 30 percent weekly) work because there is no buildup.

PPS-Pro suits keepers with shrimp tanks (which dislike big water changes) and busy schedules.

Macronutrient deficiency symptoms

Plants signal what they are missing. Read the leaves before adjusting dosing.

Nitrogen deficiency: oldest leaves turn pale green to yellow, eventually transparent. Lower stems lose leaves. The plant pulls nitrogen from old growth to feed new growth. Fix: dose KNO3 or up the all-in-one.

Phosphorus deficiency: oldest leaves turn dark green to purple, sometimes with red tinge. Lower leaves drop. Phosphorus deficiency often shows as small dark leaves on stem plants. Fix: dose KH2PO4 or up the all-in-one.

Potassium deficiency: pinholes appear on old leaves, sometimes with yellow edges. The pinholes spread and the leaf dies. This is the most common deficiency in low-tech tanks because fish waste does not supply potassium. Fix: dose K2SO4 or add a potassium-heavy fertilizer like Seachem Potassium.

Iron deficiency: new leaves come in pale yellow or white with darker green veins. Specifically affects red plants. Fix: dose Seachem Flourish Iron or up the all-in-one (most all-in-ones are iron-positive).

Calcium deficiency: new growth is twisted, deformed, or stunted. Tips of stem plants die back. Common in soft water (under 4 dKH). Fix: dose Seachem Equilibrium or raise GH with crushed coral in the filter.

Magnesium deficiency: yellowing between veins on middle-age leaves, veins stay green (interveinal chlorosis). Fix: dose magnesium sulfate (Epsom salt) at 1 teaspoon per 50 gallons.

A practical dosing schedule

For a low-tech 40 gallon with no CO2:

• Monday: dose 4 pumps of Easy Green (or equivalent all-in-one)
• Thursday: water change 25 percent, dose 4 pumps Easy Green
• Every 2 months: push a root tab next to each crypt or sword

For a medium-tech 40 gallon with low CO2:

• Monday: dose 4 pumps Easy Green plus 2 ml Seachem Iron
• Wednesday: dose 4 pumps Easy Green
• Friday: dose 4 pumps Easy Green plus 2 ml Seachem Iron
• Sunday: water change 30 percent

For a high-tech 40 gallon with full CO2 running EI:

• Monday: dose KNO3 + KH2PO4 + CSM+B
• Tuesday: dose K2SO4
• Wednesday: dose KNO3 + KH2PO4 + CSM+B
• Thursday: rest
• Friday: dose KNO3 + KH2PO4 + CSM+B
• Saturday: rest
• Sunday: 50 percent water change

Testing nutrients (or skipping it)

Most keepers do not need to test nutrients. The dosing schedule plus a weekly water change keeps nitrate at 10 to 30 ppm, which is the only number that really matters for fish health. Phosphate and potassium tests are useful when diagnosing a specific plant problem but are not part of a routine.

If you do test:

• Nitrate: API liquid test, target 10 to 30 ppm
• Phosphate: API phosphate test, target 0.5 to 2 ppm
• Iron: Salifert iron test, target 0.05 to 0.2 ppm

For more planted-tank guidance, see our aquarium plants for low light article and the aquarium CO2 injection basics guide. The /methodology page covers our planted tank trial protocol.

Frequently asked questions