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Fishician®

Dosing from a label: scale the ratio, never the guess

Wrong volume, units or product concentration can cause dosing errors. Read the full label before calculating an amount.

2 min readUpdated September 25, 2026

About this guide

Water quality

By Fishician

Published September 12, 2026

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The short answer

  • A label gives a ratio. An amount per a stated volume. It becomes a dose only when you multiply by your real volume.
  • Use the bottle in your hand. Products get reformulated and concentrated versions differ. Never dose from memory.
  • Dose to the real volume, not the tank's label size. Check whether the label calls for replacement-water volume or total system water volume.
  • Keep the label's units all the way through. Every conversion is a chance for a big mistake.
  • Right maths isn't a right treatment. It says nothing about diagnosis, species safety or interactions.
Graduated plastic transfer pipettes on a dark background
Graduated pipettes help measure small liquid quantities. Dose calculations must follow the current product label.Photo: Einwegpipetten — Gmhofmann · CC BY-SA 3.0. Resized for display.
From label to dose
  1. ReadLabel ratioAmount per stated volume
  2. TimesMeasureReal volumeDisplay or whole system?
  3. EqualsCalculateYour doseIn the label's own unit
  4. ThenMeasure outSyringe or graduatedNot a cap or kitchen spoon
  5. FinallyRecordLog itProduct, amount, volume, time, reason

Where errors hide

  • Using the tank's label size instead of its real water volume.
  • Millilitres vs teaspoons, US vs imperial gallons, drops vs millilitres.
  • Assuming a concentrated version doses like the standard one.
  • With a sump, not deciding whether the dose covers the display or the whole system.

What the maths can't tell you

  • Whether the product fits the problem, your species or your invertebrates.
  • Interactions, effect on the biofilter, maximum dose or repeat frequency.
  • Many treatments harm invertebrates; some shouldn't be combined. Read the whole label, warnings included.
  • Check water quality first. Environmental problems can cause or contribute to illness. See warning signs.

Dose deliberately

  • Add it where circulation is good, not into a filter intake or onto animals.
  • Some products are removed by activated carbon. Follow the label on whether and when to remove or replace it.
  • Record every dose. A course depends on the first one being right. See keeping records.

Measure accurately

  • Use a syringe for small volumes; caps and kitchen spoons vary.
  • Measure with something marked in the label's own unit.
  • A course of treatment usually has a schedule. Your record keeps the second and third doses right.
  • If the tank responds badly, that record is what you or a vet will need.

Sources

Each source is listed with the part of this guide it supports.