TOOL 11
Dosing
Calculator.
Work out exactly how many millilitres of fertiliser or medication to add, based on your real tank volume and the dose rate on the label. Units handled in litres or US gallons.
Required dose = tank volume × (dose amount ÷ dose basis). Double-check every label: some products dose per 10 L, others per 10 US gallons, and medication doses are often per 1 L.
ABOUT THIS TOOL
Dosing
Calculator.
Fertilisers, water conditioners, and medications all come with a recommended dose rate, usually written per 10 litres or per 10 US gallons. The problem is that few labels make it easy to convert that rate to your specific tank, especially if your volume was worked out from external dimensions or measured in a different unit. Guessing leads to underdosing that does nothing or overdosing that harms fish.
This calculator takes the two numbers on the label — the dose amount and the volume it applies to — and scales it to your actual water volume. It supports both litres and US gallons, because aquarium products are split between metric and American conventions and mixing them up is a common source of error.
Always use your true water volume rather than the tank's marketed size. Substrate, decor, and the unfilled rim mean a tank holds noticeably less water than its dimensions suggest. If you have not measured it yet, use the Tank Volume Calculator first and enter that figure here.
HOW TO USE
Using the
Calculator.
- Find the dose rateRead the label and note two things: the dose amount (for example 5 mL) and the volume it applies to (for example per 10 L or per 10 US gallons).
- Enter your tank volumeType your actual water volume, ideally from the Tank Volume Calculator, and select litres or US gallons to match.
- Set the dose rateEnter the dose amount and choose the basis — per 10 L, per 10 US gallons, or a per-litre/gallon option for concentrated products.
- Read the required doseThe primary result shows how many millilitres to add to the whole tank in one dose.
- Double-check the unitsConfirm the tank unit and dose basis both reflect the label. Unit mismatches are the single most common dosing mistake.
- Dose and observeAdd the dose, then watch fish and plants for a day or two. Adjust with experience rather than repeatedly changing the maths.
FAQ
Dosing
Questions.
Should I use litres or US gallons?
Use whichever unit the product label uses. If the label says per 10 US gallons, set both your tank unit and the dose basis to US gallons. Mixing metric and US units is the most frequent cause of dosing errors.
Is Imperial gallon supported?
This tool uses US gallons, which is the standard for most aquarium products. One US gallon is about 3.785 L while an Imperial gallon is about 4.546 L, so if a label is British, convert it first or enter your volume in litres.
Should I dose for gross or actual volume?
Use actual water volume. Dosing for the marketed tank size overdelivers, because substrate, decor, and the unfilled top reduce the real amount of water.
Does this work for medication?
Yes. Many medications dose per litre or per gallon directly, so choose the matching basis. For medications, precision matters — measure with a syringe rather than a cap, and follow the treatment duration on the label exactly.
What about daily fertiliser dosing?
If your fertiliser is dosed daily, the result is your daily amount. If it is dosed weekly or after a water change, the same figure applies on that day. Never carry a missed dose forward by doubling it.
Can I overdose safely?
No. Overdosing fertiliser fuels algae and can stress plants; overdosing medication can poison fish outright. When unsure, dose to the lower end of the label range and observe rather than exceeding it.