Thanks a lot for that.Set my mind at rest, i agree about having a control but unfortunately i don't have the funds...i'll leave it to you

haha.
I suspect you dont live in my area also where i can't find shrimp for less than £2 a go!
That's part of the "myth building machine" that is the aquarium hobby.
Few are willing to sacrifice any livestock to test anything.
Those that have trouble keeping livestock, or plant free of algae are hardly able to produce a control tank to begin with.
Even well seasoned aquarist are no different generally.
Few are willing to do such things.
However, when someone with a nice TANK OR HELATHY ANIMALS DOES A MISTAKE, LIKE THIS, now we can say something about whether or not it kills.
You have to assume that adding Iron or Copper should kill the shrimp.
That's the claim/hypothesis.
So you try and disprove it.
Once shown to be false, you reject that rational/hypothesis and make a new one for the deaths of the shrimps.
Eventually you get the choices narrowed down.
So this presents quite a pickle for learning anything new for hobbyists.
They just want to keep their critters happy, but there are many test to do to see. Ghost shrimp and soft waters make ideal cheap test subjects and all you need is small tank and keep track of how much you add and over what frequency.
Regards,
Tom Barr