Copper is toxic to fishes. My first hand experience was weighting down an air line with a copper air valve as weight and the poor datnoids were spinning in circle. They eventual died. I thought it was a bad fish at first. After a couple of datnoids died, I switching to something else and the problem stopped. That was a long time ago when I did that. That was my first experience with heavy metal poisoning to my fish. Later on I've seen the same thing happen with older fountains and ponds with copper plumbing. No fishes can leave it.