corys and bala sharks dying

Question
Please help!!  We bought some neon tetras at the local pet store, thought everything was fine, but then we noticed all 4 were gone.  Then one of my corys died, followed by the other, both Bala sharks and some other tetras.  They aren't eating as they should be.  I've done a water  change, changed the filter, added water cleaner...I don't know if the neons were diseased or what?  This is more upsetting to my kids to see at least one of their fish get flushed every morning.  Do you have any idea what may be happening?  Thanks!

Answer
The thing about tetras is they can carry a dormant disease that is deadly to other fish but it does not show any signs and cannot be treated. If the tetras are from a bad place or were breed wrong they can have the disease and once they are introduced to other fish the disease is deadly to the other fish. Did you see any signs of illness other than not eating? If not, I suspect that it was the tetras disease that was the culprit. If you did see other signs than it was something else and likely could have been treated with the right treatment. The thing about fish is that if you dont get very strong and well-bred fish they can almost always die on you. When we try to mimic nature in our little glass tanks, sometimes the result is not good. While I am sure this was a very sad time for your children, hopefully you can explain to them that this happens and now you can go and rescue some other fish and hopefully have a better result. It is very odd for the balas and corys to die so easily so whatever it was, tetra disease or other, it was a very aggressive issue and likely could not have been cured anyways. If the tank is empty now, completely clean the tank and re-fill it. Find a local store, privately owned not a chain store, that you can go and get some fish at. Start with very hardy, easy fish like platys, mollies, and algae eaters. The fun thing about playts or mollies is they are very easy breeders so your children could watch them have babies, of course requiring special care. If you decide to let your children see fish breed, only stick to one species to make it easier to handle. For example, get only platys or only mollies. Also, invest in a fish breeder net and once you see that a female is full looking, place her in the net until she lays the fry and then keep the fry in the net and remove the mother. Keep the fry in the net until they are at least 1/3 inch long or more. This might be something you would like to try. Guppies are also good breeders and very colorful. Just be sure to keep a ratio or two females per one male if you decide to try this. Otherwise, just start over and hopefully you will find some healthier fish and have better luck. Feel free to ask me anything else if you need help.