I'm am definetly no expert Kris, but I really don't see what one has to do with the other? Prime has nothing to do with correcting algae so I really don't see how it would cancel out the other?
But honestly, I've never used anything for algae except elbow grease.... so the lfs person telling you that just makes me kinda go

.
Hopefully someone will have used them and can help you better.