How much Prime per gallon?

About 0.1 mL per US gallon: Seachem's dose is 5 mL (one capful) per 200 L, or 50 US gallons, of new water.

How much Prime for a 10 gallon tank?

About 1 mL, or one cap thread, for 10 gallons of new water at the standard dose.

Can you overdose Seachem Prime?

Seachem allows up to 5× the normal dose to detoxify nitrite in an emergency, and says a double dose may be used safely for exceptionally high chloramine. Don't go beyond its table.

How much Prime for ammonia?

Seachem's table: standard dose for about 1 ppm ammonia, double for about 2 ppm, triple for 3, quadruple for 4 and the maximum for about 5 ppm.

Do I dose Prime for the whole tank or just the new water?

Seachem's dose is per volume of new water for water changes; for an ammonia or nitrite problem, treat the tank volume at the matching level.

Seachem Prime Dosage Calculator: mL, Capfuls & Threads

JavaScript is disabled in your browser, so the interactive calculator below won't run. The math, formula, and worked example are all written out further down this page under “How this is calculated.” Enable JS (or open this page in another browser) to use the live calculator.

Whether you compute by hand or in the calculator, the same caveat applies: verify against your test kit and the linked primary source before dosing. reefcalcs is reference information, not veterinary or engineering advice.

Seachem Prime

Water to treat (US gal)

Situation

Dose

0.95mL

Capfuls (5 mL each)

0.19capfuls

Cap threads (about 1 mL each)

0.9threads

For a water change, dose the volume of new water. For an ammonia or nitrite problem, dose the whole tank at the level that matches your test, and fix the cause: Seachem sells Prime to detoxify ammonia and nitrite, but it doesn't remove them, and it doesn't replace water changes or a working biofilter. Seachem's ceiling is 5× the normal dose.

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How this is calculated

mL       = litres × 5 ÷ 200 × level      (Seachem: 5 mL per 200 L; level 1–5)
capfuls  = mL ÷ 5
threads  ≈ mL ÷ 1                          (Seachem: each cap thread is about 1 mL)

Seachem's table runs from the standard dose (water changes, or ammonia around 1 ppm) through double (about 2 ppm ammonia, nitrite, chlorine or chloramine), triple, quadruple and maximum (around 5 ppm ammonia). The calculator never goes past 5×. For a water change, dose the new water; in an emergency, dose the whole tank and deal with the cause, which our ammonia page walks through.

FAQ

How much Prime per gallon?: About 0.1 mL per US gallon: Seachem's dose is 5 mL (one capful) per 200 L, or 50 US gallons, of new water.
How much Prime for a 10 gallon tank?: About 1 mL, or one cap thread, for 10 gallons of new water at the standard dose.
Can you overdose Seachem Prime?: Seachem allows up to 5× the normal dose to detoxify nitrite in an emergency, and says a double dose may be used safely for exceptionally high chloramine. Don't go beyond its table.
How much Prime for ammonia?: Seachem's table: standard dose for about 1 ppm ammonia, double for about 2 ppm, triple for 3, quadruple for 4 and the maximum for about 5 ppm.
Do I dose Prime for the whole tank or just the new water?: Seachem's dose is per volume of new water for water changes; for an ammonia or nitrite problem, treat the tank volume at the matching level.

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Sources & references

1.
Seachem — Prime dosing (manufacturer support article)
https://seachem.zendesk.com/hc/en-us/articles/115000125454
2.
Francis-Floyd, Watson, Petty & Pouder — Ammonia in aquatic systems, UF/IFAS FA16
https://extension.rwfm.tamu.edu/wp-content/uploads/sites/8/2013/09/Ammonia-in-Aquatic-Systems.pdf

Last reviewed 2026-10-29