How We Calculate Aquarium Doses
By Richard James · Updated 27 October 2026
The calculator separates physical water volume from the printed capacity of a tank. It scales a chosen product course without deciding whether treatment is appropriate.
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Three distinct volume methods
- Measured water: the actual amount entered, with no deduction.
- Nominal capacity: capacity multiplied by an explicitly chosen remaining-water fraction.
- Rectangular dimensions: internal length × width × water depth in centimetres ÷ 1000, followed by the chosen deduction.
A 50 × 40 × 30 cm water space is 60 L. A selected 15% deduction gives an estimated 51 L. Presets are estimates, not measured displacement.
Units and precision
One US gallon is 3.785411784 L; one UK gallon is 4.54609 L. Dimensions use 2.54 cm per inch. Unit changes convert the stored quantity, not just its label. The calculator retains full numeric precision internally and rounds the displayed quantity separately.
Source rate and schedules
Amount = water volume ÷ reference volume × reference amount. As a pure arithmetic fixture, 5 mL per 200 L gives 2.5 mL at 100 L. A product schedule has individual dose or action rows, not a universal three-day template.
gdex uses a five-day plan with dosing on days 1–3, no dose on day 4 and a water-change action on day 5. ndx has its own 24-hour cleanup. Read the checked gdex guide.
Rounding is product-specific
For enabled dropper products, positive whole-drop amounts round upward, matching the manufacturer calculator. Known product-specific mL equivalents use the unrounded amount. Drops and mL are alternative measures, never additive. Small quantities below the display resolution are flagged rather than silently presented as zero. Decimal precision is stated in each calculation: most liquid quantities use two decimal places, while Safe is shown in milligrams to one decimal place. Display precision does not establish that your equipment can measure the amount.
Salt concentration arithmetic
Mass in grams = water volume in litres × a concentration independently chosen in g/L. The salt tool assumes no existing salt; it does not recommend a treatment concentration or model repeated additions.
Bounds and limitations
The calculator supports 3.8–100,000 L after displacement. These are software bounds, not safety limits for livestock. It does not automatically add sump water, adjust for test results, select repeat courses or choose special label exceptions.
Inspect sources and review status
Every enabled product shows its source and check date. Unverified entries show no dose. See the source model, review policy and backlog.