Seachem Prime vs API Stress Coat
Two water conditioners that both dechlorinate tap water but earn their keep in different ways. Seachem Prime is the ultra-concentrated safety net that also detoxifies ammonia; API Stress Coat adds aloe vera to protect the fish's slime coat. Here's which one belongs on your shelf — or whether you want both.
The quick verdict
These aren't really rivals — they're a pair. Reach for Seachem Prime as your everyday conditioner: it's the most concentrated on the shelf and its ammonia/nitrite detox is a real safety net when a tank spikes. Reach for API Stress Coat when you're adding, moving or nursing fish and want the aloe slime-coat protection. If you can only buy one, buy Prime.
| Seachem Prime | API Stress Coat | |
|---|---|---|
| Removes chlorine/chloramine | Yes | Yes |
| Detoxifies ammonia/nitrite | Yes (~24–48 h) | No |
| Aloe slime-coat protection | No | Yes |
| Dose | 5 mL per 200 L | 5 mL per 38 L |
| Concentration / value | Very high, lasts months | Modest |
| Cycling safety net | Yes | No |
| Best for | Every change + emergencies | New or stressed fish |
Ammonia detox vs slime-coat protection
The one big difference is what each does beyond dechlorination. Prime temporarily converts free ammonia and nitrite into a non-toxic bound form for roughly 24–48 hours, which is genuinely useful during a spike or a fish-in cycle — it buys time while your filter bacteria catch up. Stress Coat has no such trick; instead it adds aloe vera to protect and help rebuild the slime coat, the mucus layer that shields fish from infection and abrasion after netting, transport or a scrape. Different problems, different tools.
Concentration and value
Prime also wins decisively on economy. At 5 mL per 200 L it's so concentrated that a single 500 mL bottle conditions around 5,000 L of tap water — months of weekly changes even on a big tank. Stress Coat is dosed much heavier at 5 mL per 38 L, so you get through it faster. Both are easy to over-pour by eye, so use the cap.
Our pick
For an everyday, do-everything conditioner, Seachem Prime is the one to own — cheaper per litre, and the ammonia safety net no plain dechlorinator matches. Keep API Stress Coat alongside it for the stressful moments when fish need the aloe. Read the full Seachem Prime review and API Stress Coat review, or see the whole range on our water testing hub.
Frequently asked questions
Is Seachem Prime or API Stress Coat better?
They do different jobs. Both remove chlorine and chloramine, so either makes tap water safe. Prime's edge is that it temporarily detoxifies ammonia and nitrite, making it a genuine safety net during a spike or a fish-in cycle. Stress Coat cannot do that, but it adds aloe vera to protect the fish's slime coat. Many keepers own both: Prime for routine changes and emergencies, Stress Coat for new or stressed fish.
Which one should I use while cycling a new tank?
Prime. Its temporary ammonia and nitrite detox is exactly what buys you time during a fish-in cycle or a spike. Stress Coat dechlorinates new water but does nothing about ammonia, so it should never be your only line of defence while a tank is cycling. Keep testing with a liquid kit either way.
Which lasts longer per bottle?
Prime, by a wide margin. It doses at just 5 mL per 200 L, so a 500 mL bottle treats around 5,000 L of tap water. Stress Coat doses at 5 mL per 38 L, so a 237 mL bottle treats around 1,800 L. Prime is far more concentrated and cheaper per litre of water treated.
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