Copper is a heavily toxic substance which should be avoided in an aquarium at any means. It’s nonsense to speak negatively about “chemicals” and positively about copper.
In Germany we use “Flubenol” against Hydra with a success of 100% and no risk for delicate fish at all. I do not know which is the name for the white powder in other countries. Mixed substances which are composed of that substance including others for the sake of other purposes should be avoided; try to get the pure Flubenol. It may be diffcult to find; you certaily will not find it in pet shops. Try special chemical dealers in the internet. The smallest amount will be enough for many years.
Using it in practice, you only need the smallest amount of it (a knife’s tip), it will spread over the water surface immediately and two or three days later all Hydra are gone. Hours after application you see the first reaction already. Even if you use it in double or triple quantity it will do no harm to the fish.
With any form of copper you play vabanque with the ecosystem of your tank.