Lost All My Fish Overnight

Foster_16

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My family and myself run a small saltwater aquarium shop. We have a 300 gallon 8 foot display tank that lost all its fish inhabitants overnight.. i don't get what happened; when I closed the shop last night all the fish were perfectly happy and healthy like they've always been. (We don't sell the fish in the display tank, they are ours) We had a beautiful unicorn tang that my dad has had for almost 5 years; one of the best looking clarkies you'll ever see, a gorgeous healthy comet, a little sixline, a fox face, yellow tang, and a very expensive achilles tang.. All of them gone overnight.

The salinity is at an exact 1.025, N & P's both next to none and untraceable amounts of ammonia. No signs of any stray electric currents.. Ive been doing this for a while and I wash my hands every time before I have to put them in a tank, and even then the only time I put my hands in this tank yesterday was to drop in their dinner like every night. The skimmer has some bubbles in it but nothing alarming, and I don't smell any sort of soap or chemical coming from it. And even more, the inverts and corals are all still perfectly fine. I would have figured if anything was contaminating or otherwise harming the tank the inverts would have been first to go, yet they are all still alive while everyone of our fish are dead. It was horrible this morning seeing these fish that we've had for years and years just all dead in one night with no apparent cause. Anyone have any ideas what could be wrong in our tank, because we are all stumped..
 
Could a customer have put something in the tank? Sadly I see this occasionally posted.

The tank is canopy'd off and behind our counter.. And our shop is small enough that Im pretty much always in range of everyone in the store.. I also have no clue what could have been added to the tank that would only kill the fish but not any of the corals and inverts
 
did the fish show any signs of disease? velvet? when was the last time you added anything?

No visible signs of diseases on any one.. No sores, spots, respiratory signs.. nothing. Cant think of a disease that would kill every fish in the same night with no previous symptoms either. Last time I added anything to the tank was just adding new water into it after a water change on saturday. Im really at a loss.

Skimmer and jets were all still running this morning and we have a power monitor that alerts us if the power goes out.. So i don't think it could have been O2 depletion.
 
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Did you check all heaters to see if they are functioning properly? I had one crack and electrocute all my fish about 10 years ago.
 
So sorry to hear that. If all the equipment is working properly, it had to have been something put in the water. Some PETA weirdo maybe?
 
What inverts are/were in the tank? A cucumber could cause death to fish and not to inverts; a sea apple can do the same thing.

I suspect a toxin
 
All heaters and equipment are woking like they should, no sign of shock.. Inverts in the tank are a shrimp, a 2 foot brittle star, a beatiful big red log tentacle that the clarky was living in, there are 3 sea cukes, but they are a forskali and 2 edulis, both of which im fairly certain are non toxic.

My only guess is something had to have poisoned them but I cant for the life of me figure out what could kill all the fish overnight and not at all harm anything else
 
Rob Toonen said:
As for being poisonous, I would have to say that there is really no such thing as a completely non-toxic sea cucumber, because nearly every species that has been tested to date appears to possess chemical defenses against at least some species of predators (e.g., Bryan et al. 1997, reviewed by Paul 1992; Pawlik 1993)

there are 3 sea cukes, but they are a forskali and 2 edulis, both of which im fairly certain are non toxic.
There's your problem.
 
I agree with Hunter. I never have and never will keep cucumbers (aside from the one an lfs suckered me into when I was a newbie.)
 
how awful for you, i'm so sorry! my first thought was some sort of chemical poisoning, too, but surely that would have also killed your inverts. :(
 
There's your problem.

Yes most, possibly all, cukes have some sort of chemical defense but as far as anything ive ever known about these 2 kinds I have were that their defense was more to make them less palatable, nothing fatal let alone wipe out an entire tank. Ive had them for over a year without a problem and they all seem to be doing fine now.. You really think it was them?
 
What inverts are/were in the tank? A cucumber could cause death to fish and not to inverts; a sea apple can do the same thing.

I suspect a toxin

timing suggests a toxin although I cannot say it was or was not a sea cucumber.
 
http://www.fishchannel.com/saltwater-aquariums/species-info/invertebrates/sea-cucumbers.aspx

"Another way certain sea cucumbers could be lethal to your fish is if they die in your tank, or if they are damaged by a piece of mechanical equipment (like powerhead impellers), as happened in your situation. If this should happen, the toxin could be released from the body wall or internal organs. Finally, the gametes of some sea cucumbers are toxic and if they are consumed by your fish, the fish will perish."

If you had two edulis, perhaps they tried to spawn and the fish ate the gametes?

"Other cucumbers that have been reported to kill fish if injured or stressed include the pink cucumber (Holothuria edulis)"
 
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