Plant care calculator

Aquarium fertiliser Calculator: Get Your Exact Macro and Micro Nutrient Dose

Written by PlantSolve Editorial Team · Published

Calculate exact macro and micro fertiliser doses for your planted aquarium based on tank volume, plant density, CO2 system, and dosing strategy.

Quick Answer

This calculator is for planted aquariums, not ordinary houseplant pots. It scales fertiliser dosage by aquarium water volume, dosing strategy, plant density, and CO2 setup so aquatic plants receive nutrients without pushing unnecessary algae risk.

  • Input plant type, pot size, and fertiliser type for a custom dose.
  • Get precise mixing amounts instead of guessing dilution strength.
  • Adjust results based on growth stage and current plant health.
  • Use the calculator to avoid common fertiliser burn mistakes.
Last reviewed: 2026-08-14 Reading time: 7 min

Enter your details

Use the actual water volume after substrate, hardscape, and equipment displacement.

Static Reference

Static Reference:

Visible baseline values

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
EI planted aquarium dosing Macro 5 ml per 20 gal/week and micro 5 ml per 20 gal/week before plant-density and CO2 adjustment. High-energy method; pair with stable CO2, consistent light, and 40-50% weekly water changes.
PPS-style lean dosing Macro 7 ml per 10 gal/week and micro 7 ml per 10 gal/week before density and CO2 adjustment. Dose smaller amounts consistently and watch algae response for 2 weeks.
Low-tech aquarium dosing Macro 2 ml per 20 gal/week and micro 1 ml per 20 gal/week before density adjustment. Best for low-light tanks without pressurized CO2.

Methodology: Formula pattern: weekly_dose_ml = tank_volume_gal x strategy_base_rate x plant_density_multiplier x co2_multiplier. Macro and micro channels use independent base rates, then output a practical schedule with algae-risk caution when energy inputs are high.

The Problem

Planted aquarium dosing is easy to over- or under-estimate because nutrient demand changes with water volume, plant mass, light intensity, and CO2 availability.

When to Use This Tool

Use this calculator when setting up a planted aquarium, changing fertiliser methods, increasing plant density, adding CO2, or troubleshooting algae and slow aquatic plant growth.

Who is this for?

  • Planted aquarium keepers comparing EI, PPS-Pro, and low-tech fertiliser routines
  • Aquascapers adjusting nutrient dosing for plant density and CO2 availability

About this calculator

Aquarium plant fertiliser dosing depends on water volume, light energy, plant density, and CO2 availability. This calculator gives a practical baseline for planted tanks.

How to Use

  1. Enter the aquarium's real water volume in litres.
  2. Choose the dosing strategy that best matches your tank: EI, PPS-Pro, or low-tech dosing.
  3. Select plant density and CO2 setup to adjust the macro and micro dose estimate.

Why Aquarium Volume Matters

Aquatic fertiliser is diluted through the entire water column. A 20 litres planted tank and a 75 litres planted tank need different total doses even when they use the same fertiliser method. CO2 and plant density change uptake speed, while low-tech tanks usually need leaner dosing to reduce algae pressure.

Visual Reference: Healthy Aquatic Growth

Lush planted aquarium

High-Tech Planted Tanks: When dosing macros and micros correctly using the Estimative Index (EI) or PPS-Pro methods, your aquatic plants should display rich, deep colors without any string algae or green spot algae on the glass or older leaves.

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Aquarium fertiliser Dosing Methods Compared

MethodBest ForWater Change NeedDifficulty
Estimative Index (EI)High light, CO2-injected planted tanksWeekly 40-50%Moderate
PPS-ProLean daily dosing and stable planted tanksSmaller regular changesModerate
Low-tech dosingLow light tanks without injected CO2Routine maintenanceEasy

Troubleshooting & Diagnostics Guide

1 Algae increases after dosing

Diagnosis: The tank may have too much light, unstable CO2, excess nutrients for the plant mass, or inconsistent water changes.

Treatment: Reduce light intensity or duration first, keep CO2 stable if injected, maintain regular water changes, and lower dosing strength until plant growth catches up.

Glossary of Terms

Transpiration
The process of water movement through a plant and its evaporation from aerial parts.
Photoperiod
The period of time each day during which an organism receives illumination.

Scientific References

  1. Aquatic Plant Fertilization — Aquatic Gardeners Association
  2. Nutrient Dosing in Planted Aquaria — The Aquarium Wiki

Frequently Asked Questions

Is this calculator safe for fish and shrimp?
Yes — the baseline dosages are heavily diluted to be safe for livestock. However, if you have highly sensitive shrimp, start at 50% of the recommended dose. Always monitor livestock behavior after dosing.
Is this accurate for low-tech aquariums?
Yes. By selecting the 'Low-tech' dosing strategy, the calculator drastically reduces macro and micronutrients to prevent algae outbreaks in tanks without injected CO2.
Should I dose daily or weekly?
It depends on your strategy. PPS-Pro requires lean daily dosing, while the Estimative Index (EI) usually alternates macros and micros every other day. Breaking up the total weekly dose stabilizes water parameters.
Do I need to do water changes when dosing?
Yes, especially if using the EI method. You must perform a 50% water change weekly to reset nutrient levels and prevent toxic build-up.
Can I mix macro and micro fertilizers together?
No. Mixing concentrated macros (Phosphates) and micros (Iron) in the same bottle causes them to precipitate and become unusable by plants. Always dose them on alternating days or space them out by several hours.
Why am I getting algae after dosing?
Algae blooms indicate an imbalance between lighting, CO2, and nutrients. Often, the light is simply too intense for the available CO2. Reduce your lighting period by 2 hours before altering your fertiliser routine.
Why are my plant leaves turning pale despite dosing?
Pale leaves typically signal a nitrogen or iron deficiency. Ensure you are shaking your fertiliser bottles well before dosing, and double-check your tank's true water volume to ensure you aren't under-dosing.
How often should I recalculate my fertiliser dosage?
You should recalculate whenever you significantly trim your plants, upgrade your lighting, or add CO2. A change in light directly alters how fast plants consume nutrients. Try our Sunlight Calculator to verify your light intensity.