While there are some good points made here, re temperature changes, it can affect some fish badly.
I once refilled my Congo tetra tank too quickly (I don't have any mixer taps or a shower
) during a 60% change and when I'd refilled to about 80% I glanced in the tank to check everything and my Congos were in what looked like fits; most of them were upside down and barely swimming. I honestly thought I'd killed the lot of them. They recovered fairly rapidly, but other fish might not have.
I once refilled my Congo tetra tank too quickly (I don't have any mixer taps or a shower
) during a 60% change and when I'd refilled to about 80% I glanced in the tank to check everything and my Congos were in what looked like fits; most of them were upside down and barely swimming. I honestly thought I'd killed the lot of them. They recovered fairly rapidly, but other fish might not have.
