I replace the evaporated water in the sump, when I do the water change, so I add the prime to both the sump and the tank. Enough in each location for the volume of the Tank or sump.
I mention this as relevant because my bio media is in the sump, I have yet to see any indications of a mini cycle. So I must assume the water is safe faster then it can do harm to the bio media or the fish. If it was harming the bio media, then the weekly 50% WC would cause an endless mini cycle.
While I don't test the water I see no signs of ammonia or nitrite poisoning, which I have seen first hand and know what it looks like.