Pumps always should be tested in tap water and kept running for 5-10 minutes, or however many that are recommended in the instructions. This is to remove the oils and grease that help make sure that the product has a long shelf life, along with keeping it from drying up on the inside. The part that probably killed your fish was the excess oil/grease that intoxicated the fish.
In the best interest, remove the pump now and clean it out, while also doing a good water change on the tank to save the koi angels from death. I am sorry to hear that this happened to you, but i hope that many of us can learn form this experience.
I have never had this product before, so i no idea about this product in particular.
Roses are red,
Violets are purple,
Or are they blue?
I love my fish,
and so should you!