By adding new fish directly to your main tank you have exposed all the fish to whatever diseases or parasites the new ones brought with them.
Quarantine. Always.
A month in isolation would have allowed you to see some medical problems and treat without risking all your fish.
OK... What this sounds like...
There is a very common fish bacterial disease called Flavobacteria columnaris. It looks at first like a bit of color loss or white-grey discoloration. The many forms give it different names, often including the word 'Fungus'. One of the forms is so virulent it can kill within 24 hours. Most often it spreads over the surface of the fish body, but can also attack the fins. It is one of the causes of fin rot.
There are antibiotics specifically for fish that can treat this. Look for antibiotics that treat Gram negative bacteria.
This is not the only thing that might look like this, but it is the most common.
The stringy poo sounds like an internal parasite. Fish get 'worms' just like dogs and cats. Similar medicine can kill these parasites.
What to do...
This is a tricky one. Your established fish might be healthy enough to fight off the columnaris, so I would not start antibiotics on them unless they show signs of disease. Then isolate in the q-tank and treat.
All the fish have potentially been exposed to parasites that made to poo stringy in the one. These parasites (there are many species) generally grow slowly, shed eggs or other reproductive means and spread among the population. The whole tank is considered infested. I would treat with something like Prazi Pro, Levamisol or other wormer. If you can get any ID on what it is you can target the medication to the worm and get the best results.
Quarantine. Always.
A month in isolation would have allowed you to see some medical problems and treat without risking all your fish.
OK... What this sounds like...
There is a very common fish bacterial disease called Flavobacteria columnaris. It looks at first like a bit of color loss or white-grey discoloration. The many forms give it different names, often including the word 'Fungus'. One of the forms is so virulent it can kill within 24 hours. Most often it spreads over the surface of the fish body, but can also attack the fins. It is one of the causes of fin rot.
There are antibiotics specifically for fish that can treat this. Look for antibiotics that treat Gram negative bacteria.
This is not the only thing that might look like this, but it is the most common.
The stringy poo sounds like an internal parasite. Fish get 'worms' just like dogs and cats. Similar medicine can kill these parasites.
What to do...
This is a tricky one. Your established fish might be healthy enough to fight off the columnaris, so I would not start antibiotics on them unless they show signs of disease. Then isolate in the q-tank and treat.
All the fish have potentially been exposed to parasites that made to poo stringy in the one. These parasites (there are many species) generally grow slowly, shed eggs or other reproductive means and spread among the population. The whole tank is considered infested. I would treat with something like Prazi Pro, Levamisol or other wormer. If you can get any ID on what it is you can target the medication to the worm and get the best results.
