I am talking about a new tank. That the cycle was just ending. Not a overstocked established tank which your filters are well established. UV is not recommended during a cycle. If you are talking about "putting a bandage on a bullet wound" your tank should be clear with out a UV. I f you want to talk about carbon--- Fill up a white bucket with water from a tank using carbon and a bucket not using carbon. Anyone can see right away the obvious difference. I was just recommending a natural product thats been around longer then us. I did not mean to offend anyone or to make this an argumentative issue.