, the correct thing to do is a fishless cycle.
But since we already have the fish, then (again IMHO
) the correct thing to do is ONLY daily PWC
to keep the ammonia and nitrite levels low. The amount of the PWC
depends upon the ammonia and nitrite levels. You might find that one day the levels are particulary high and you need to do a 50% water change, and another day you might find the levels are already low and you decide to either to a small (10%) PWC
or skip it all together.
If you are treating the TANK water with chemicals, then you won't know what the actually levels are (as bs6749 pointed out) and therefore not know how much of a PWC
However, you still want a bottle of Prime. Assuming that you are refilling the tank with city tap water, you need Prime to pre-treat the city water to neutrilize the various forms of chlorine used to treat city water as well as neutrilize any ammonia and nitrites in the city water. In this case, you only use two drops per gallon. That will be enough to prepare the water to add to your tank, but it's not enough to effect the ammonia and nitrite levels in your tank.