Fish Emergency In Established Tank.

[geezerloca]

Established tank has dying fish.
Only new element is 3 small fish from a celebration here in community. No visible signs of disease on these new ones. They seemed to adjust okay. Then just started dying. Now one of the original residents is dead. No symptoms or visible sign of malaise.
Lol, sorry.
Tank has been established for just under 4 yrs. I am seeking information/help for my 7yr old grandson. (which is why I do not sound emotionally attatched. He, however has been in tears with every loss poor guy.) We have a placostamus, and two fancy goldfish. The fish brought home from the celebration were goldfish (feeder fish my son explains). The tank is a 30 gallon tank.
My Son is 'Guardian of the tank' and does not, to my knowledge, test the water. He does partial changes, and the tank is filtered and aerated.
The new goldies were pretty small and the smallest was the first casuality. We think the bigger ones may have been tempted, or he simply got caught in the pump because the poor little guy was missing his entire tail. The other two have died a few days apart, with no visible sign. They had been moved to a smaller, filtered, aerated tank for safety. Today we found our big black Gold fish dead. Cause unknown. Help our sad little Boy?
PS.. Blackie was in the large tank.

 

[fluttermoth]

Can you please tell us;
 
the size of the tank?
 
how long it's been set up ?
 
exactly what fish (species and numbers) are in there?
 
have you tested the water at all?
 
Sorry for all the questions, but we can't tell, from the information you've given, what might be happening. The more information we have, the better we can get to the root of the problem

 

[geezerloca]

Thank you for guidance. I apologize for the lack of information. I amended my post to reflect more information. Thank you.

 

[fluttermoth]

It's still not possible to say for sure what is happening, but here's my best guess.
 
Fish produce ammonia, in their wastes. In the normal run of things, there are bacteria living in the filter that eat the ammonia and stop it turning the water bad (ammonia is very toxic to fish). As long as the insides of the filter are never washed in tap water, only in old water from the tank, those bacteria should carry on doing their job.
 
But, if you add a lot of new fish in one go, there aren't enough bacteria to eat all the ammonia, and it builds up in the water.
 
You'll need to do some large water changes (at least 50%), and get some test kits ASAP. Nearly all fish health problems turn out to be water related, as test kits are something no fishkeeper should be without.
 
You can get your fish shop to test the water for you, but get them to write the numbers down for you. All too often they'll say, "it's fine", or "a little high", and that's of no use to anyone.
 
But, water changes are the first thing that needs to be done. Make sure the new water is temperature matched and dechlorinated.
 
I'm so sorry for your grandson, it's very upsetting for kids to lose pets

 

[Liv15]

Sounds like it could be ammonia / poor water quality from the addition of new fish. Water changes need to be done with use of a dechlorinator / tap safe product

 

[TwoTankAmin]

Feeder goldies have a reputation of being swimming death traps. Most experienced fish keepers will have nothing to do with them. They will breed their own feeder fish instead.
 
Diagnosing fish is usually hard to difficult and often impossible. But, given the circumstances here, I would be expecting a total tank wipeout, unfortunately. If one has no idea what is wrong, its hard to treat for that. At best it would be a guess and given the rapidity of the deaths I am not sure how to treat.
 
If you want to take a shot, get a broad spectrum antibiotic ASAP and follow the directions to the letter. If you have carbon in your filter, remove it before medicating. You need test kits, especially the ammonia one.
 
I wish I could offer a more positive assessment.