Best Fertiliser Calculator Apps for Planted Aquariums
Overdosing iron turns your water tea-brown; underdosing nitrogen starves your carpeting plants into pale misery. A good fertiliser calculator app for your aquarium removes the guesswork by converting tank volume, target ppm, and fertiliser concentration into precise millilitre doses. This is a tool we use constantly at Gensou Aquascaping in Singapore, where our heavily planted display tanks demand accurate nutrient management week after week.
Why You Need a Dosing Calculator
Planted tank fertilisers vary wildly in concentration. A 5 ml dose of one brand’s iron supplement might deliver 0.1 ppm, while the same volume of another delivers 0.5 ppm. Manually crunching the maths every water change is tedious and error-prone. Calculator apps handle the arithmetic instantly, letting you focus on observing your plants rather than wrestling with spreadsheets.
Rotala Butterfly — The Community Favourite
Rotala Butterfly is a free browser-based calculator trusted by thousands of planted tank hobbyists worldwide. It supports the Estimative Index (EI), PPS-Pro, and custom dosing regimes. Punch in your tank dimensions, select your fertiliser brand, and the app spits out daily or weekly dose volumes in millilitres. The interface is straightforward, though it can feel cluttered on a phone screen.
APT Calculator by 2Hr Aquarist
Developed right here in Singapore by Dennis Wong of 2Hr Aquarist, the APT Calculator is tailored to the APT fertiliser line. It factors in your lighting intensity and CO2 level to recommend a starting dose, which is more nuanced than a flat EI approach. For hobbyists already using APT Complete or APT EI, this is the most seamless option available.
Aquarium Fertiliser Calculator by Aqua Tools
This Android app offers offline functionality — handy when you are dosing at a friend’s place or a local fish shop without reliable Wi-Fi. It covers most major fertiliser brands and lets you save multiple tank profiles. The free version includes ads, while the paid upgrade at roughly $4 removes them and unlocks cloud backup of your dosing history.
Spreadsheet-Based DIY Calculators
Veteran hobbyists sometimes prefer a custom Google Sheets calculator. You control every variable: dry salt purity, water volume after hardscape displacement, even evaporation loss between doses. Building one takes an afternoon, but the flexibility is unmatched. Several templates circulate on local forums and the Singapore Planted Tank Facebook groups — search for “EI dosing spreadsheet SG” to find a well-maintained version.
Comparing Accuracy Across Apps
We tested three apps dosing potassium nitrate into a 60-litre tank. Rotala Butterfly and the DIY spreadsheet agreed within 0.2 ppm; the APT Calculator matched when we set the correct APT product concentration. Discrepancies usually stem from users entering gross tank volume rather than actual water volume after subtracting substrate and hardscape — a common mistake that inflates doses by 10-15 %.
Tips for Getting the Most From Your App
Measure your actual water volume by logging how many litres you add during a complete refill rather than relying on the manufacturer’s stated tank size. Update your app inputs whenever you change substrate depth or add a large piece of driftwood. Singapore’s soft PUB tap water (GH 2-4) means you may need to dose more calcium and magnesium than hobbyists in harder-water regions — factor GH targets into your calculator if the app supports it.
Which App Should You Choose?
If you use APT fertilisers, start with the APT Calculator for its tailored recommendations. For EI or PPS-Pro dosing with dry salts, Rotala Butterfly is hard to beat. Power users who enjoy fine-tuning every variable will get the most from a custom spreadsheet. Whichever tool you pick, the real value comes from consistent use — dose accurately, observe your plants, and adjust based on what the leaves tell you.
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