Welcome to the forums and TFK first of all
I suspect the reason the person at the fish store suggested you put Copper Sulfate in the tank at each water change is as an ICH prevention. Copper Sulfate is used in a lot of ich medications.
Long term though it will kill almost any plants you have in the tank and is also bad for fish.
It will also treat internal parasites and this is perhaps what they also suggested using it for.
Long term though I seriously would not use it or any other form of treatment until it is absolutely necessary, I have been keeping cichlids for 14 years and have never once heard of copper sulfate being used to aid digestion until you posted it here.
Copper Sulfate long term is extremely toxic to ALL aquatic life. It is fine using it for ich medication but NOTHING else.