Seachem Prime Dosage Guide
If you keep a freshwater or saltwater aquarium, knowing the right Seachem Prime dosage is one of the most useful skills you can have. Prime is a concentrated water conditioner that removes chlorine and chloramine and temporarily detoxifies ammonia, nitrite, and nitrate — but only if you dose it correctly. This guide breaks down the standard dose, emergency dosing, a tank-size chart, and the mistakes that trip people up.
What Is the Standard Seachem Prime Dosage?
The standard Seachem Prime dosage is 1 capful (5 mL) for every 200 liters (about 50 US gallons) of new water. The cap on the bottle doubles as the measure: a full cap is 5 mL. For most hobbyists doing a partial water change, you dose Prime for the volume of new water being added, not the whole tank. Always add a quality conditioner like Seachem Prime to tap water before or as it enters the tank to neutralize chlorine and chloramine instantly.
Seachem Prime Dosage Chart by Tank Size
Use this quick reference for treating a full water volume. For partial water changes, dose only for the new water added.
| Tank / Water Volume | Standard Prime Dose |
|---|---|
| 5 gallons (19 L) | ~0.5 mL (about 10 drops) |
| 10 gallons (38 L) | ~1 mL |
| 20 gallons (76 L) | ~2 mL |
| 50 gallons (200 L) | 5 mL (1 full capful) |
| 100 gallons (400 L) | 10 mL (2 capfuls) |
Emergency Dosing for Ammonia and Nitrite
During an ammonia or nitrite spike — common in a tank that is not fully cycled — you can safely use up to 5x the standard dose (5 mL per 10 US gallons) to temporarily detoxify those compounds for about 24–48 hours. This buys time but is not a substitute for fixing the underlying problem. If you are seeing spikes, read our nitrogen cycle guide and learn how to cycle a new aquarium. Prime detoxifies ammonia for roughly 24–48 hours, so re-dose daily until your cycling method catches up.
Using Prime During Water Changes
Most fish losses after maintenance come down to untreated tap water or temperature shock — see why fish die after a water change for the full list of causes. Dose Prime for the new water before adding it, match temperature, and go slow. When introducing new livestock, follow proper fish acclimation steps rather than dumping bag water in.
Prime for Shrimp and Sensitive Species
Prime is invertebrate-safe at the standard dose, but shrimp react badly to swings, so dose conservatively and keep parameters stable — our shrimp water parameters guide covers the targets. If you are adjusting chemistry, also review the aquarium pH guide so a conditioner change does not mask a deeper issue.
Common Seachem Prime Dosing Mistakes
Overdosing “just in case.” More is not better; stick to label rates outside of a genuine ammonia emergency. Dosing the whole tank on every water change. For partial changes, treat only the new water. Forgetting it is concentrated. Prime is far stronger than cheap conditioners, so a little goes a long way. Relying on Prime to replace cycling. It detoxifies temporarily — it does not establish a biofilter.
Where to Buy Seachem Prime
We stock Prime in multiple sizes — the 100 mL, 250 mL, and 500 mL bottles. Browse the full Seachem collection or compare options in our water conditioners collection.
Frequently Asked Questions
How much Seachem Prime per gallon? About 0.1 mL per gallon at the standard dose (5 mL per 50 gallons). A full cap is 5 mL.
Can you overdose Prime? Prime is forgiving, and up to 5x is considered safe for emergencies, but routinely overdosing is unnecessary and can reduce oxygen in the short term.
How often can I dose Prime? You can re-dose every 24–48 hours during an ammonia emergency. For normal use, dose with each water change.
Does Prime remove ammonia permanently? No. It detoxifies ammonia and nitrite temporarily (about 24–48 hours). Only a cycled biofilter removes them for good. Track those levels with one of the best aquarium test kits.