I am at my wits end. Two years ago I put in a preform garden pond. After struggling with various issues I removed it and put in a round dug pond that is about 8 ft across and about 28 inches deep about 8 months ago. It has a strong pump on it pushing water through a tuba center piece and a filter. The filter is electric that is supposed to have ultraviolet light to kill algae. Over the past 8 months I have probably put in excess of 100 fish. A mixture of koi and goldfish. They have all come from pet stores and were mostly 35 cents. Two days ago someone gave me 3 large koi/goldfish. They were about 12 inches long. I was so hoping that these would make it. They were transported about 45 miles in a tub filled with water and an air pump. They seemed to be ok. One was dead less than 20 hours later. The other 2 were dead this morning less than 48 hours later. I have had the water tested by the pet stores and everything was in the normal range. I want fish in this pond so bad. After putting the fish in 2 days ago I put some water clarifier in that said it was safe for fish. My daughter said she did some research and said it could be the copper and zinc in the brass of the tuba. I suppose that could be it. I don’t know what else to do. I would buy as many as 30 of the 35 cents ones knowing at least half of them would be gone within two days. I am open to any suggestions. I just don’t know what else to do.