My Koi are dying, they are swimming erratically upside down and back and forth darting one end to the pond and the other. and smashing into the rocks and the side of the pond. they are not rubbing, it seems like they are trying to get out of the water. some fish have died. others are affected. water quality is good nitrates and nitrites are non existent. i've done numerous water changes, ph was a little low i've raised it a bit. more than enough aration temp stays within range.. i'm lost for answers. I need help fast. anybody have any answers?