Everything dead apart from CUC, no idea whats happened!

[FishTruck]

Did you check the salinity of the new water? Before and after the WC?

Did you check the salinity of your Chromis (make sure they weren't living at 1.017 like my shipments seem to be?).

A bump in salinity can take fish out with dramatic quickness - as I have learned by making a stupid mistake once or twice.

 

[lstmysock11]

Do you have anything like a sea cucumber in the tank? Just read when they die they will release a toxin that will kill just about everything in the tank. Either way good chance something very toxic got in the tank in that water change. Clearly not a sickness since that test fish died in under a minute.

 

[vetteguy53081]

How can fish be electrocuted in water? Electricity always flow throw the least resistance way. Fish are surrounding by highly conductive saltwater. I can't think of a practical case where the electricity will flow throw the body of a fish other than through the water. Unless the fish body has substantially lower resistance than saltwater?

This stray voltage, even in small amounts, can cause several subtle or dramatic problems in an aquarium. Sometimes, aquarists have tested for stray voltage leaks in their tanks after experiencing sudden and otherwise inexplicable losses of fish and found that a faulty appliance in their tank was the cause. There have been faulty tank heaters on the market that have resulted in the complete loss of all fish and/or invertebrates in saltwater aquariums.
When continuous strange behavior such as a rapid and jerky swimming pattern or frequent quivering of tank inhabitants is observed, many aquarists have discovered that the cause was stray voltage. Fish have sensors on their bodies, such as along the lateral line and on their noses, which are sensitive to changes in electricity in the water around them. When these sensors receive a continuous supply of abnormally high electricity, it throws their systems out of kilter. Also one cause of lateral line erosion.

 

[vetteguy53081]

To test for stray voltage :
- Purchase or borrow a voltage meter. They can generally be found for less than $20 at most automotive parts or hardware stores
- Turn the selector to "120 AC Voltage."
- Insert the tip of the black probe into the third or "grounding" hole in an electrical outlet
- Insert the metal tip of the red probe into the aquarium water
- Watch the meter needle for any movement. Any needle movement indicates a voltage leak in your system. Digital meters will show a number reading.

How to Identify the Voltage Leak Source:​

- One at a time, disconnect each electrical appliance (heaters, pumps, lights, chiller) associated with your aquarium, retesting for voltage as described above after each unit is disconnected.
- Heaters and water pumps (powerheads) are the most frequent cause of voltage leaks. These devices have 120 volts of electricity feeding into them, which is enough to do a lot of damage in a saltwater aquarium.

 

[Mical]

I'm with the group that suspects water contamination of some sort. My first guess would be water from LFS.

 

[00W]

So sorry man. My thoughts go out to you.
Sounds wierd and I'd never admit this happened but I lost a whole tank years ago using an anti bacterial sponge cleaning my tank. I think I cleaned out my bucket too. It was a 100 gallon and I was changing about 25percent at the time and pretty much the same thing happened.
I don't know how big your tank is but 25 percent at a small tank size would hurt.
Just a thought and I've never told anyone I did this. I felt so bad.

 

[mvbrandt]

I would stop trying to test for stray voltage. The net evidence doesn't support that diagnosis at all.

 

[lstmysock11]

Have you made any progress on fixing this? Finding the problem? Sure something toxic got in your tank.