Help fish died after changing gravel

Unfortunately I killed my fish... but have no idea how. Changed the gravel in my tank and my 5 tetras and 1 molly were dead within 5 hours. I'd love some help to figure out what may have happened. What did I do wrong? I feel terrible and want to avoid this ever happening again.

Tank has been fully cycled for over a year. Wanted to change the gravel from the weird orange/green gravel to black. Was given advice at the store that I'd be ok to change out the gravel if I left the other media in the tank and left the filter alone. So that's what I did. Took about 50% of the water, it in a bucket along with the fish. 30 minutes later had the gravel switched out and added the fish and media back.

A few hours later, all the Tetra were lying dead at the bottom and not too long after, the Molly was dead. I feel horrible. I have no idea what I did wrong. Maybe it's obvious but I'm not sure what the mistake was. I certainly want to avoid this ever happening again.

Was this most likely a toxin I introduced into the tank? All the fish were healthy prior to this.

Any help in determining what I did wrong would be greatly appreciated.

 

Disturbing all the gravel could have caused a big ammonia spike as detritus was released.

What size is the tank and what type of filter do you have?

 

5 tetras and a molly wouldn't produce that much ammonia that quickly. This wasn't an ammonia spike.

Im betting that you had hydrogen sulfide gas built up in the substrate that was released into the water once the gravel was disturbed.

 

It is a 10 gallon Top Fin from Petsmart. We've been using the filter that came with the set. It's a Silentstream 10.

We checked the parameters right after discovering the fish. Everything seemed to be ok. Ammonia and nitrites were both at zero. The day after the water became very cloudy, but is back to normal now.

5 tetras and a molly wouldn't produce that much ammonia that quickly. This wasn't an ammonia spike.

Im betting that you had hydrogen sulfide gas built up in the substrate that was released into the water once the gravel was disturbed.

Certainly sounds like something that could have killed the fish that quickly. Though we didn't disturb the gravel too much until we had removed most of the water and added the fish to the bucket. Then took everything, including gravel and remaining water out, before adding in new gravel and finally the fish.

 

Taking all the fish out then the gravel and water should have been ok. Maybe you forgot dechlor? That could do it too. Just checking boxes.

 

Certainly sounds like something that could have killed the fish that quickly. Though we didn't disturb the gravel too much until we had removed most of the water and added the fish to the bucket. Then took everything, including gravel and remaining water out, before adding in new gravel and finally the fish.

Did you dechlorinate the new water?

You say that you "didn't disturb the gravel too much" before you took the fish out...but you did disturb the gravel (?) A little bit before you took the fish out?

How often were you gravel vaccing this tank previously?

 

Did you dechlorinate the new water?

You say that you "didn't disturb the gravel too much" before you took the fish out...but you did disturb the gravel (?) A little bit before you took the fish out?

How often were you gravel vaccing this tank previously?

btw, thanks so much for the replies everyone.

Yes we probably disturbed the gravel a little bit before getting the fish out. We've been vacuuming the gravel every couple of weeks prior to this.

We did add Prime when the new water was added.

 

btw, thanks so much for the replies everyone.

Yes we probably disturbed the gravel a little bit before getting the fish out. We've been vacuuming the gravel every couple of weeks prior to this.

We did add Prime when the new water was added.

Im still leaning towards toxic gas release.

But lets shift gears a bit...
Tell us exactly how you rinsed the new gravel before adding it to the tank.

 

Im still leaning towards toxic gas release.

But lets shift gears a bit...
Tell us exactly how you rinsed the new gravel before adding it to the tank.

I put the gravel into a bucket, let the water start to overflow, then continued to move the gravel through my hands until I stopped seeing a lot of dust and particles come up. We did not use boiling water.

Also, this might be normal with black gravel... but as I rinsed it, the bucket as well as my hands were getting black. Obviously some of the paint/coating used was coming off. The gravel was Imagitarium black gravel from Petco

 

Don't change gravel. The substrate is the lifeblood of the aquarium. You replace it you are essentially starting a new tank

 

Don't change gravel. The substrate is the lifeblood of the aquarium. You replace it you are essentially starting a new tank

Well....we're way passed that now

 

Don't change gravel. The substrate is the lifeblood of the aquarium. You replace it you are essentially starting a new tank

If that had a significant effect that caused the death of the fish, then there should be an ammonia and/or nitrite spike though.

 

If that had a significant effect that caused the death of the fish, then there should be an ammonia and/or nitrite spike though.

Right, we're talking about a few tetras and a molly in 10 gallons.
They were dead after 5 hours. No mini-cycle advances that quick....and the tests were at 0ppm.

 

Well....we're way passed that now

Wouldn't have made the change if I knew it was going to end with 6 dead fish

Really bummed, as that Molly had been such a trooper. We're new to fish keeping as of about a year and a half ago. She was the first fish we ever put in the tank and she just kept on truckin'. Whatever happened 2 days ago took all the fish out in a flash.

I'd like to get the tank back going, and move to a planted tank. Should I remove the black gravel to be safe? Is it possible there was an issue with it?

 

Ammonia is not the only issue in fishkeeping. Things like pH crash, sudden depletion of oxygen, and release of volatile organics in the substrate, just to name a few of the issues with big substrate changes

 

We also added a black background that same day. I feel sheepish now... obviously shouldn't have made so many changes at once. Would these things have caused enough stress on the fish to take them all out that fast?

 

Wouldn't have made the change if I knew it was going to end with 6 dead fish

Really bummed, as that Molly had been such a trooper. We're new to fish keeping as of about a year and a half ago. She was the first fish we ever put in the tank and she just kept on truckin'. Whatever happened 2 days ago took all the fish out in a flash.

I'd like to get the tank back going, and move to a planted tank. Should I remove the black gravel to be safe? Is it possible there was an issue with it?

What others suggest about releasing something toxic can make sense, though would be rare given that you completely removed everything. But there may be ways it remained trapped. Not sure how because if any was released into the water you have the fish in, sounds like it could not be too much though. And any remaining after the gravel change since you removed all the water wouldn't be much either. So kinda perplexed. Not saying not possible, just perplexing.

The other possibility I am leaning towards is the new gravel itself and maybe it is toxic. I am unfamiliar with the product so can't say for certain though, and a quick google search seemed to say it is perfectly fine. Maybe it is a bad product, but again, can't say for certain. Just odd to see such quick deaths.

Ammonia is not the only issue in fishkeeping. Things like pH crash, sudden depletion of oxygen, and release of volatile organics in the substrate, just to name a few of the issues with big substrate changes

When saying lifeblood it did not sound like you were talking about release of organics or anything else, that sounds less about being a lifeblood or not, and more about trapping deadly stuff or not.

 

We also added a black background that same day. I feel sheepish now... obviously shouldn't have made so many changes at once. Would these things have caused enough stress on the fish to take them all out that fast?

Well I can promise you that the new background didn't kill your fish.
So don't count that as one of the things that contributed.

If you disturbed something toxic in the gravel and it released into the water....then you put that water in a bucket with the fish.....that's the only thing that I can logically think of because I'm pretty sure that your new gravel (that you rinsed perfectly) is just fine.

Nevertheless, your filter is still cycled. I would add a few small fish soon.

 

Well I can promise you that the new background didn't kill your fish.
So don't count that as one of the things that contributed.

If you disturbed something toxic in the gravel and it released into the water....then you put that water in a bucket with the fish.....that's the only thing that I can logically think of because I'm pretty sure that your new gravel (that you rinsed perfectly) is just fine.

Nevertheless, your filter is still cycled. I would add a few small fish soon.

Makes me feel a bit better.

The only other thing I can think of, which may be a bit of a stretch, is I bought a new 5 gallon bucket and dust pan for the job. I didn't think to rinse either of those off before starting. That is the bucket I added the fish to while I changed the gravel. Maybe that bucket was the culprit?

 

We also added a black background that same day. I feel sheepish now... obviously shouldn't have made so many changes at once. Would these things have caused enough stress on the fish to take them all out that fast?

Yes definitely. These small fish can die from stress alone

When saying lifeblood it did not sound like you were talking about release of organics or anything else, that sounds less about being a lifeblood or not, and more about trapping deadly stuff or not.

These organics eventually breakdown to be food for plants which in turn goes back to help the fish. They also provide the carbon source for many heterotrophic bacteria including some nitrifiers and some de-nitrifiers (if this activity does indeed occur in aquariums)

More importantly, in acidic envrionments these decomposing compounds ie humic acid actually provide the bicarbonates that act as the buffer of the system

So imo there are many important factors associated with an "aged" substrate

 

Right, we're talking about a few tetras and a molly in 10 gallons.
They were dead after 5 hours. No mini-cycle advances that quick....and the tests were at 0ppm.

I was more suggesting that if the gravel was filled with detritus, etc that all that "gunk" released into the water column could have been more than the established bacteria could handle. Wasn't suggesting that the fish would release enough ammonia afterwards.

Regardless, based on the additional information that seems less likely. Could have been some freak toxic gas or something in the transfer bucket. Otherwise I'm not sure how it could have happened so quickly.

 

Maybe that bucket was the culprit?

It's a stretch. Cant really say.

 

How often do you usually do water changes and how much?

 

How often do you usually do water changes and how much?

Typically we do a 25-30% water change every other week.

 

If you disturbed something toxic in the gravel and it released into the water....then you put that water in a bucket

I am wondering if something toxic wasn’t in the bucket. Maybe it had nothing to do with the tank or changes at all and someone accidentally used that bucket to clean or it was new and had something in it from the factory like manufacturing oils or other toxins.

 

I am wondering if something toxic wasn’t in the bucket. Maybe it had nothing to do with the tank or changes at all and someone accidentally used that bucket to clean or it was new and had something in it from the factory like manufacturing oils or other toxins.

He said it was a brand new bucket, but he didn't rinse it. Again....it's a stretch, but not impossible.
Those pesky manufacturing oils!

 

We've been vacuuming the gravel every couple of weeks prior to this.

This almost certainly ensures there was no toxic build up of any sort in your gravel bed. It's the substrates that never get disturbed that are more likely to go toxic. And it's not hydrogen sulfide it's deadly bacteria that gets released when finally disturbed.

 

Make sure you are not adding way more Prime than called for. It can deplete O2 when overdosed. A lot of people say it's a myth, but not according to Seachem. The question is how much is too much. Normal and emergency dosing are OK per the instructions, but if someone made a math mistake, and did huge overdose it could cause problems. Seachem says that you can use up to 5x the recommended dose for emergency Nitrite situations.