oppssss sorry...I was just reading the first page...didn't know there were more than 1 page...i am sorry you lost your koi...as I have said, levels of ammo and nitrite more than 0.25ppm are detrimental to fishes in long terms. Fully cycled tanks should have ammonia=0ppm, nitrite=0ppm, and nitrate=5-40ppm...Cycling with fish is a little work since you need to make sure that the levels are okay for your fishy residents. To make sure the levels are okay, you have to check it everyday and when it is higher than 0.25ppm, you have to change the water 50-70% at least once a day. Before I did it 2-3 times a day since I have a koi and 2 fancy goldfish and 2 plecos. They are heavy bioloaders (which would raise ammonia more than normal)...hence the PWC is VITAL.