Aquarium dechlorinator calculator

Read the current bottle. Seachem specifies 5 mL (one capful) per 50 US gallons of new water. Its rounded metric label is not an exact conversion of that ratio. When Prime is added directly to the aquarium, Seachem says to base the dose on the aquarium volume. The small change dose here assumes separate treatment in a container. Other products and formulations have different doses; no API dose is assumed. Generic formula: water gallons × label mL ÷ label gallons.

Worked example: 20 gallon long

Prime standard US label ratio: 5 mL ÷ 50 US gal = 0.1 mL/gal. Full nominal fill: 20 × 0.1 = 2 mL. A 25% change of estimated working water: 20 × 0.85 × 0.25 = 4.25 gal; dose = 0.42 mL when treating that new water separately.

Seachem Prime directions — checked November 3, 2026. This calculator covers standard dechlorination, not emergency dosing.

Choose a tank size

• 2.5 gallon12 × 6 × 8 in
• 5 gallon16 × 8 × 10 in
• 5.5 gallon16 × 8 × 10 in
• 10 gallon20 × 10 × 12 in
• 13 gallon widescreen24 × 8 × 19 in
• 15 gallon24 × 12 × 12 in
• 15 gallon column13.75 × 13.62 × 25 in
• 20 gallon high24 × 12 × 16 in
• 20 gallon long30 × 12 × 12 in
• 20 gallon extra high20 × 10 × 24 in
• 25 gallon24 × 12 × 20 in
• 29 gallon30 × 12 × 18 in
• 30 gallon36 × 12 × 16 in
• 33 gallon long48 × 13 × 13 in
• 37 gallon30 × 12 × 22 in
• 38 gallon36 × 12 × 20 in
• 40 gallon breeder36 × 18 × 16 in
• 40 gallon long48 × 12 × 16 in
• 45 gallon36 × 12 × 24 in
• 50 gallon36 × 18 × 19 in
• 55 gallon48 × 13 × 21 in
• 60 gallon breeder48 × 18 × 16 in
• 65 gallon36 × 18 × 24 in
• 75 gallon48 × 18 × 21 in
• 90 gallon48 × 18 × 24 in
• 110 gallon48 × 18 × 30 in
• 120 gallon48 × 24 × 24 in
• 125 gallon72 × 18 × 21 in