I bought 3 Ryukin goldfish and 2 died within 8 hours, what could have happened?
My tank is new, had been up and running empty except for 1 live plant for a week, I had Petsmart test the water before buying my fish. I added 3 Ryukin goldfish and 2 algae eaters yesterday at about 1:30 and by 11 pm 2 of the goldfish had died. The 3rd is swimming about and the algae eaters seem fine also. I have the proper air pumps and I just can't understand why they would die so fast? They were not picking on each other either... after I let them float in the tank for 15-20 min, I released them and they seemed fine for about 2 hours then I saw that one was at the top of the tank a lot with his tail pointing to the bottom... the other one seemed to hide in the cave a lot... the 2 fish that died came out of the same tank... could they have been sick already? I'm wondering if they may have had swim bladder and if so could that kill them that fast? I noticed about 8 pm that they were sitting near the bottom of the tank and one was in the cave, I thought maybe they were just resting... I had to go out and when I came back a couple hours later I found both of them were dead but the 3rd fish was fine swimming about as were the algae fish... so strange!
Any help would be greatly appreciated, I am new to the aquarium scene, I haven't had one for about 25-30 years (when I was a kid) and want to learn quickly so as not to harm any future fish.