Prime Review
The most concentrated dechlorinator on the shelf: removes chlorine and chloramine, detoxifies ammonia and nitrite, and doses at just 5 mL per 200 L — one small bottle lasts months.
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👍 Pros
- Removes chlorine and chloramine and binds heavy metals in tap water
- Detoxifies ammonia and nitrite temporarily — a genuine safety net during a spike
- Extremely concentrated: 5 mL treats 200 L, so a 500 mL bottle lasts a long time
- Works in fresh and saltwater, so one bottle covers any tank
👎 Cons
- Has a faint sulphur smell some people dislike
- Easy to overdose if you eyeball it — use the cap or a syringe
- Ammonia detox is temporary (~24–48 h), not a substitute for water changes
The one bottle every keeper reaches for
Seachem Prime is the most widely recommended water conditioner in the hobby, and it earns it two ways. First, it does the core job — stripping chlorine and chloramine out of tap water and binding heavy metals — so every water change is safe for fish and for your filter bacteria. Second, it temporarily detoxifies ammonia and nitrite, which turns it into a genuine safety net during a spike or a fish-in cycle.
Concentrated to the point of lasting forever
The headline is the dose: 5 mL treats 200 litres. That makes a 500 mL bottle enough to condition around 5,000 litres of tap water, so even a big-tank keeper doing weekly changes gets months out of one bottle. The trade-off is that it is easy to overdose if you pour by eye — use the cap or a syringe. There is also a mild sulphur smell, which is normal and harmless.
Where it sits in a new setup
Prime is the treatment half of a day-one kit: use it on every bucket of new water, and lean on its ammonia detox while a bottled starter such as Dr Tim’s One & Only seeds your filter. Watch the numbers with the API Freshwater Master Test Kit so you know when the cycle is done. More options are on our water testing hub; pair it to the right tank on the aquariums page and the filters hub.
The benchmark conditioner: cheaper per litre than anything else because it is so concentrated, and the ammonia/nitrite detox makes it a safety net no other dechlorinator matches.
Prime — frequently asked questions
How much Prime do I dose?
The standard dose is 5 mL (one capful) per 200 litres / 50 US gallons of new tap water. For a heavy chloramine supply or during an ammonia emergency you can safely go up to 5× that dose. Add it to the new water at each water change, or to the whole tank volume when setting up.
Does Prime really neutralise ammonia?
It converts free ammonia and nitrite into a non-toxic bound form for roughly 24–48 hours, which buys you time during a spike or a fish-in cycle. It does not remove them — your filter bacteria still process them, and Prime does not stall the cycle. It is a safety net, not a replacement for water changes.
Is a conditioner really essential?
For almost everyone, yes. Municipal tap water contains chlorine or chloramine that is toxic to fish and to the beneficial bacteria in your filter. A dechlorinator like Prime makes tap water safe instantly, so it is a genuine day-one essential alongside a test kit.
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