Newbie pond owner with multiple dying fish unknown reason

[CaitlinRose]

I've had no problems up until three days ago with my pond. I originally had (sorry I don't know fish names) 3 catfish of some sort only baby sized, 3 small orange thin fish, four goldfish, 3 of those orange, black and white look alike goldfish and one different catfish (named victor) i have a 110 litre pond with a pump and a filter all which work perfect to keep the water clear and clean no problems for the last six months I've had it in i recently bought the 3 catfish and the 3 look alike goldfish and since then all hell as broken loose. The three catfish died on the exact day swimming around fine and then the next hour floating just dead. That night one of the look a like goldfish and the orange thin fish died and now my poor victor is swimming slow, not eating and isn't seeming to swim straight. His head is up but swims on an angle.

Ive had the fish for over six months the six new fish though are what started everything. When i got the three look alike goldfish from the pet store the lady said they had just been put in the tank and that's why one was floating and dead it was stressed. I did the normal thing and put the plastic bags of fish in the pond until the water in both was the same temperature and i did a test for ammonia and nitrates and everything was tip top in shape.

Did i get a dud couple of fish that had a disease? I just need to know because I'm losing all of my fish horribly fast and it's hurting me to see my poor babies die and I can't do anything to help.

Currently im sitting on 2 thin orange fish, victor, two look alike goldfish and my four goldfish thank you to anyone that can help me.

 

[Matt68005]

Sounds like columnaris. If you could get your hands on some Terramycin (oxytetracycline) antibiotic pellets in the future you could stop bacterial diseases like this before they get too bad. Im not sure where your from, but heres an example.
Ken's Premium Sinking Pellets with Oxytetracycline 2.5mm

 

[CaitlinRose]

Thank you. I think I'll be lifting my pond out of the ground and give it a good cleaning as well as quarantine my fish for a while hopefully that will help as well. I'll try to find pellets like the ones you've shown. Thank you again!