Seachem Prime almost killed all our fish

Be very careful when using concentrated water conditioner and always try to add less than the recommended dose
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Our fish tank was having an ammonia spike around 0.5 ppm and we Googled how we can lower it. People on forums were talking about Seachem Prime and we’ve read positive reviews about it.

We went to PetSmart and bought one. We read the instruction and used 1 capful. The fish looked fine the first few minutes and we thought it won’t harm them. We had lunch and when we came back, almost all of our fish are dead. It was really shocking to see how fast it happened. Probably less than 30 minutes.

Some fish that were still alive started to jump out of the fish tank. According to Seachem Prime instruction, it is safe to use even 5x the amount. 1 capful was for 50gal and we have 35gal, so even if it’s only a little but more, it should be fine.

But it seems like it was dangerously high and it instantly depleted all the oxygen in the water, suffocating all the fish. The product should at least have a warning about this.

We were trying to save our fish and we ended up killing almost 80% of them. Really tragic and sad day.

Instead of saving them, we ended up burring them in our backyard. RIP fishes.


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To be honest, I don’t think it was the prime that killed your fish. I think you didn’t use enough prime. You essentially used a dose for new water, as if you were neutralizing tap water to top up your tank. Double dose is for tap water with higher than usual chloramines. 5x is for emergencies such as what you were experiencing. So the fish likely died from ammonia and nitrite poisoning. I have used prime to save fish a few times. I used the 5x dosage though.

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