SO i had a 15 gal tank with 2 large Common Goldfish in it for over a year, i recently upgraded to a really nice 50 gal tank and got new gravel (washed it), a new Bio-Wheel filter, live plants from the orignial tank (so i know theyre safe) and a air-bubble rod. I added PondStart water conditioner (for stress and slimecoat) and i added a dechlor, and let the tank circulate for a day. upon adding my 2 Common Goldfish, I also added the original water from their tank to help acclimate the fish to the new tank. Everything went really, the fish were fine for over a week until randomly the largest one died. There were no signs of bad health or disease and they had both been eating fine. Since the other goldfish was alone in a 50 gal tank, I added 3 Ryukin (fancy) Goldfish, 1 Commet goldfish, and one more (small) Common Goldfish. Everyone was doing fine except for the largest Ryukin, he was floating around at the top, sometimes upside down, and gasping for air. I thought he would be dead by morning, but the next day i found him swimming around and in perfect condition. One week later, i awoke to find my smallest Common Goldfish dead. Again, no prior signs of bad health or sickness. He swam around fine, ate normally, and was not bullied or chased by the other fish. I cant seem to figure out these random deaths and they continue to happen one by one, does anyone have any thoughts or suggestions? Thanks so much.