We keep the levels of Cu in our fish systems at 50% of treatment strength, I can't imagine a LFS keeping it any higher then that for long periods of time, as it is hard on the fish.

That being sad, treatment strength is .50 PPM, so it is VERY little CuSO4 when you consider the overall volume of water.

If he added only 3 cups of water, that had .5ppm of copper in it, to lets say 40 gallons of water (accounting for sand/rock) then I doubt very highly he will see ANY adverse effects at all in his tank.

Now, if he added 3 cups of CuSO4 to his tank directly, EVERYTHING would be dead in minutes.

Tell him not to worry...