Liquid Fertiliser for Aquariums: Complete Dosing Guide

Table of Contents

• Why Aquarium Plants Need Fertiliser
• All-in-One vs Individual Dosing
• Macronutrients vs Micronutrients
• Popular Brands Available in Singapore
• Dosing Methods: EI vs Lean
• Building a Dosing Schedule
• Signs of Over-Dosing and Under-Dosing
• CO2 and Light Balance
• SGD Cost Comparison
• Frequently Asked Questions

Why Aquarium Plants Need Fertiliser

Aquatic plants require the same essential nutrients as terrestrial plants: carbon, nitrogen, phosphorus, potassium, iron and a suite of trace elements. In nature, these nutrients are continuously replenished through decomposing organic matter, mineral-rich substrates and water flow from nutrient-laden sources. An aquarium, by contrast, is a closed system with limited nutrient input.

Fish waste provides some nitrogen and phosphorus, but rarely in the quantities or ratios that plants need for optimal growth. Micronutrients like iron, manganese and boron are almost entirely absent from tap water. Without supplementation, plants gradually starve — showing yellowing leaves, stunted growth, pinholes and eventually melting away. Liquid fertiliser bridges that gap, delivering dissolved nutrients directly into the water column where stems, epiphytes and floating plants can absorb them through their leaves.

All-in-One vs Individual Dosing

All-in-One Fertilisers

All-in-one (AIO) products combine macronutrients and micronutrients in a single bottle. You dose one product and receive a balanced nutrient profile. This approach is convenient, beginner-friendly and sufficient for the vast majority of low-tech and moderate planted tanks.

Popular examples include APT Complete by 2Hr Aquarist, Tropica Premium Nutrition and Seachem Flourish Comprehensive.

Individual Dosing

Advanced hobbyists and high-tech tank owners sometimes prefer to dose each nutrient separately — potassium nitrate (KNO3), potassium phosphate (KH2PO4), potassium sulphate (K2SO4) and a trace-element mix. This allows precise control over each nutrient level and is the basis of the Estimative Index (EI) dosing method.

Individual dosing is more cost-effective at scale but requires more knowledge, more bottles and more discipline. For most hobbyists, an all-in-one product is the sensible starting point.

Macronutrients vs Micronutrients

For a detailed guide to identifying specific deficiency symptoms with visual references, see our aquarium plant deficiency guide.

Popular Brands Available in Singapore

APT by 2Hr Aquarist (Singapore Brand)

Founded by Singapore aquascaper Dennis Wong, 2Hr Aquarist produces the APT range — arguably the most popular planted-tank fertiliser line in Southeast Asia. The range includes:

• APT Zero: Micro-only, for tanks with high bioload providing sufficient macros
• APT Complete: All-in-one with full macro and micro dosing — the most popular choice
• APT EI: Higher concentrations for EI-style dosing in high-tech tanks

Being a local brand, APT products are readily available in Singapore shops and online, with no import wait times.

Tropica

• Tropica Premium Nutrition: Micronutrients only — suitable for tanks where fish waste provides sufficient macros
• Tropica Specialised Nutrition: Complete macro and micro formula for demanding plants

Seachem Flourish

• Flourish Comprehensive: Broad-spectrum micro and trace elements
• Flourish Nitrogen, Phosphorus, Potassium: Individual macro supplements
• Flourish Iron: Standalone iron supplement
• Flourish Excel: Liquid carbon source (not a fertiliser per se, but often used alongside)

ADA

• ADA Green Brighty Neutral K: Potassium supplement
• ADA Green Brighty Mineral: Trace elements
• ADA Green Brighty Nitrogen: Nitrogen supplement

ADA products are premium-priced but highly regarded in the competitive aquascaping community.

Dosing Methods: EI vs Lean

Estimative Index (EI) Dosing

Developed by Tom Barr, EI dosing takes a “never let nutrients run out” approach. You dose generous amounts of macros and micros throughout the week, then perform a large (50%) water change at the end of the week to reset nutrient levels and prevent accumulation.

Advantages: Plants never experience deficiency; simple once you establish a routine; works extremely well for high-tech tanks with CO2 injection and strong lighting.

Disadvantages: Requires large weekly water changes (non-negotiable); uses more fertiliser; can fuel algae if light or CO2 is inadequate.

Lean Dosing

Lean dosing provides just enough nutrients to meet plant demand without significant excess. This approach relies on careful observation — adjusting doses based on plant health, growth rate and any deficiency symptoms that appear.

Advantages: Lower fertiliser consumption; smaller water changes acceptable; lower algae risk from excess nutrients.

Disadvantages: Requires more experience to read plant signals; risk of deficiency if under-estimated; less forgiving in high-tech setups.

For most Singapore hobbyists running low-tech to mid-tech tanks, lean dosing with an all-in-one product like APT Complete is the practical sweet spot.

Building a Dosing Schedule

Low-Tech Tank (No CO2, Low-Moderate Light)

High-Tech Tank (CO2 Injected, Strong Light)

Always follow the manufacturer’s recommended dosage as a starting point, then adjust based on plant response over several weeks.

Signs of Over-Dosing and Under-Dosing

Under-Dosing Signs

• Yellowing or pale leaves (nitrogen or iron deficiency)
• Pinholes in older leaves (potassium deficiency)
• Stunted or slow growth despite adequate light
• Thin, spindly stems
• Plants losing lower leaves

Over-Dosing Signs

• Algae outbreaks — particularly green dust, green spot or hair algae
• Cloudy water shortly after dosing
• Excessive biofilm on water surface
• Shrimp showing signs of stress (though this is rare with quality fertilisers at normal doses)

If in doubt, under-dosing is safer than over-dosing. You can always increase gradually, but removing excess nutrients from the water requires water changes.

CO2 and Light Balance

Fertiliser, light and CO2 form a triangle of interdependent factors. Providing generous fertiliser without adequate light and carbon means plants cannot utilise those nutrients — and algae will. Conversely, high light and CO2 without sufficient fertiliser will lead to nutrient deficiency and stressed plants.

The golden rule: match your fertiliser dosing to your light and CO2 levels.

• Low light, no CO2: Dose conservatively. Plants grow slowly and need less.
• Medium light, no CO2: Moderate dosing. Consider liquid carbon (Flourish Excel or equivalent) to bridge the carbon gap.
• High light + CO2: Full EI or manufacturer-recommended dosing. Plants are growing rapidly and consuming nutrients quickly.

SGD Cost Comparison

DIY dry-salt dosing is by far the cheapest option for high-tech tank owners, though it requires a precision scale and some initial learning. For most hobbyists, an all-in-one product offers the best balance of convenience and cost.

Frequently Asked Questions

Is liquid fertiliser safe for fish and shrimp?

Yes, when dosed according to manufacturer instructions. Reputable aquarium fertilisers are formulated to be safe for livestock at recommended concentrations. Copper-sensitive invertebrates like Caridina shrimp may be more vulnerable to extreme overdosing, so accuracy matters — but normal doses are safe.

Should I dose fertiliser on the same day as a water change?

It is best to dose after your water change, not before. Dosing before a water change means you are removing a portion of the nutrients you just added. After the water change, dose your regular amount to replenish nutrients in the fresh water.

Can I use liquid fertiliser in a tank with no live plants?

There is no benefit to dosing fertiliser in a fish-only tank. Without plants to absorb the nutrients, you are simply adding compounds that will feed algae. Save your fertiliser for planted setups.

How long does a bottle of liquid fertiliser last?

This depends on your tank size and dosing frequency. For a typical 60-litre planted tank dosed 2-3 times per week, a 300 ml bottle of APT Complete or Tropica Specialised lasts roughly 2-3 months. Larger tanks consume proportionally more.

Optimise Your Planted Tank

Choosing and dosing the right liquid fertiliser is one of the most impactful steps you can take for a thriving planted aquarium. Start with an all-in-one product, follow the manufacturer’s dosing guide, and adjust based on what your plants tell you.

If you need help selecting the right fertiliser for your setup, or want us to assess your tank’s nutrient balance, visit Gensou at 5 Everton Park, Singapore. We stock a wide range of fertilisers and can recommend a dosing plan tailored to your aquascaping setup.

Related Reading

• How to Mix Dry Fertiliser for Your Planted Aquarium
• Do Aquarium Plants Need Fertiliser? A Simple Answer
• Best Liquid Fertilisers for Planted Aquariums
• Best Liquid Fertilisers for Aquarium Plant Growth Compared
• Active vs Inert Substrate: Which Is Right for Your Planted Tank?