Help! Advice needed urgently about my kois/goldfishes.?

I change 10 percent water of my 10,000lt garden koi pond last night and replace it with tetra treated water. This morning i found the fishes surfacing once in a while in longer time and gasping for air. I catched some to check and their gills and section of body are unusually red and they look sluggish as I know if you catch one it will try to jump much or wriggle out of the net. I also did some manual vacuuming last night where the vacuum siphoned the dirt but stirred also the muck at the bottom and I was thinking they are affected by it. I have no way of testing the water from ammonia/nitrate so I need to know any quick solution. Must I remove all the fishes and put in my indoor holding tank and replace some of the pond water? Honestly the pond is in a state of green algae infestation and it is almost a month old and never clarify at all since the beginning tho the water never smell. It is only this morning that the fishes seem like struggling. I would appreciate your quick advice as I don't want to lose some of the fishes we had that originally started from the indoor tank.If I transfer the fishes to the holding tank, how would I treat them?I am quite in the dark as why this is happening overnight? Thanks for any advice.