Seachem Prime — Concentrated Water Conditioner for Reef and Freshwater Aquariums

Seachem Prime is the best-selling water conditioner in the aquarium hobby for a simple reason: one bottle handles chlorine, chloramine, ammonia, nitrite and nitrate in your tap water, in both freshwater and saltwater tanks. Prime is non-acidic and will not impact your aquarium's pH.

How Seachem Prime works

Every dechlorinator breaks the chloramine molecule apart, but most stop there — leaving the freed ammonia in your tank. Prime takes the next step: it contains a binder that renders ammonia, nitrite and nitrate non-toxic while keeping them fully available to the beneficial bacteria in your biofilter. Nothing is removed from the water; everything stays neutralized for up to 48 hours while your biological filtration does its job. Prime also detoxifies heavy metals found in tap water at typical concentration levels. That is why it can be used during tank cycling: it protects fish without ever stalling the nitrogen cycle.

Official Seachem dosing

Use 1 capful (5 mL) for each 200 L (50 US gallons) of new water. For smaller volumes, each cap thread is approximately 1 mL. Add Prime to new water first when possible; if dosing the aquarium directly, base the dose on total tank volume. For exceptionally high chloramine concentrations, a double dose may be used safely. To detoxify nitrite in an emergency, up to 5 times the normal dose may be used. If the water temperature is above 30 °C (86 °F) and chlorine or ammonia levels are low, use a half dose. A sulfur odor is normal.

Six sizes, from nano to fish room

Prime is up to 5x more concentrated than competing products. At the official dose of 5 mL per 200 L, each size treats: 50 mL → 2,000 L of water, 100 mL → 4,000 L, 250 mL → 10,000 L, 500 mL → 20,000 L, 1 L → 40,000 L and 4 L → 160,000 L. The 50 mL bottle covers months of nano water changes; the 4 L jug is the pick for fish rooms and large reef tank systems. Pick your size from the menu above.

Prime and ammonia test kits

A Nessler-based test kit will give a false ammonia reading when Prime is in the water. With a salicylate-based kit, take the reading right away. Seachem recommends its MultiTest Ammonia kit, which uses a gas-exchange sensor unaffected by Prime and distinguishes dangerous free ammonia from total ammonia.

How much does Prime actually detoxify?

Our advice

Prime works very well at the recommended doses, but in saltwater there is one drawback to know about: it can throw your protein skimmer off. The skimmer starts overflowing after dosing. So it is not always ideal on a reef tank — you are always better off starting with RO/DI water from day one. — Stéphane, ReefSolution

Complementary products

For transporting and quarantining fish, Seachem recommends StressGuard, and when adding new fish, Seachem Stability — the nitrifying bacteria designed to pair with Prime. The SureStart pack bundles the start-up essentials in one purchase. And if you are setting up a reef tank, an RO/DI unit produces pure water that removes the need for a conditioner at water change time.

Seachem Prime FAQ

How much Seachem Prime should I use in my aquarium?

1 capful (5 mL) for each 200 L (50 US gallons) of new water. Each cap thread is approximately 1 mL for smaller volumes. A double dose is safe for very high chloramine; up to 5x the dose in a nitrite emergency.

Does Prime stall my aquarium cycle?

No. Prime binds ammonia into a safe, non-toxic form that remains fully available to your bacteria. The cycle keeps running normally.

How long does Seachem Prime last in the water?

Prime binds ammonia, nitrite and nitrate for up to 48 hours. If they are still present after that window, they are released back unless you re-dose. Prime can be re-dosed every 24 to 48 hours.

Why does Prime smell like sulfur?

The distinct sulfur smell is completely normal and can vary between batches with no effect on how the product works. Stored properly, Prime lasts indefinitely.