Yes copper is very potent. If you have very low KH water, it may even be more potent/deadly. I know this is true for regular copper sulphate, but I'm not absolutely sure about chelated copper sulphate (Coppersafe).
The probelm with the cheleated material is that it doesn't stay that way long. So essentially the cheleated copper will break down and then has all the problems, concerns and effects of other copper products. It's called coppersafe, it just isn't.
O.K. Now to the crux of the matter, copper is already in you system. My personal reccomendation would be to get it out of there ASAP to prevent the garaunteed breakdown of the cheleated form and cause you trouble. However that was not your question either. so:
Copper will remain indefinately and will kill ich, snails, shrimp,crayfish, and eventually reptiles amphibians or fish as long as it is there. I am not familiar with the exact directions on coppersafe, but generally any time a water change is done it is assumed that we removed the same percentage of meds, and should dose accordingly. Copper on the other hand tends to stay in a system no matter what and for that reason I would not add any at water change times (Someone may correct me if this is bad advice). You have now found the primary downside to using coppersafe. How much did you remove with your water change and how much should you add back in. It is a mystery that is hard to answer without a lab grade copper test, and one that has lead to many a dead fish over the years.
In the most sincere way, I wish you luck with this product. Pay attention to your Kh level as mentioned and consider the situation fully.
Dave