The dosing formula
Every label dose is a concentration: an amount of product per volume of water. Scaling it to your tank is simple proportion. The only common mistakes are using the tank’s nominal size instead of its real water volume, and dosing the whole tank when the label means only the new water.
Your dose = label amount × your volume ÷ label volume
1 US teaspoon = 4.93 ml · 1 ml ≈ 20 drops
Worked example: water conditioner
Seachem’s directions for Prime are 1 capful (5 ml) for each 200 L (50 US gallons) of new water, and note that each cap thread holds about 1 ml. If added straight to the aquarium, Seachem says to base the dose on the aquarium volume.
A tank with 45 L of real water: 5 × 45 ÷ 200 = 1.1 ml, about 22 drops. For a 20 L water change with the conditioner added to the new water: 5 × 20 ÷ 200 = 0.5 ml.
| Water to treat | Dose | In drops (≈) |
|---|---|---|
| 10 L | 0.25 ml | 5 |
| 20 L | 0.5 ml | 10 |
| 45 L | 1.1 ml | 22 |
| 100 L | 2.5 ml | 50 |
| 200 L | 5 ml | 100 |
Kitchen and lab measures
| Measure | Millilitres | Note |
|---|---|---|
| 1 drop | ≈ 0.05 ml | Dropper sizes vary |
| 1 US teaspoon | 4.93 ml | NIST conversion factor |
| 1 US tablespoon | 14.79 ml | 3 teaspoons |
| 1 US fluid ounce | 29.57 ml | 6 teaspoons |
Dose safely
- Read the whole label. Medicines may need repeat doses, carbon removed, UV switched off or extra aeration.
- Watch oxygen. Many treatments reduce oxygen; increase surface movement while dosing.
- Do not mix treatments unless the manufacturer says it is safe.
- Remove invertebrates if the product is unsafe for shrimp or snails, as many copper-based medicines are.
- When in doubt, ask a vet or aquatic specialist, especially for sick fish.
