
Hello!
Welcome to R2R...
Best of luck to you and your tank(s).
To be as direct and simplistic as possible regarding your lights...
Lighting and how much of it is dependent on a number of variables.
Your water quality is critical in determining how much PAR, and PUR is available for your corals, inverts and algae. Just because you have strong lighting, it does not guarantee that the full intensity of the light will be necessarily available at any given point in time. A PAR meter will illustrate this concept.
Turbidity and gelbstoff are two elements that affect water clarity which, ultimately, lead to the amount of necessary light being delivered, or not, into your tank.
You also have to decide on what kind of corals and inverts you plan on purchasing now and in the near future.
Coral placement within your tank must also be looked at and factored in, when deciding if a single AI Prime HD pendant is sufficient.
By taking the time to address these issues, you will be better apt to get the most out of your light and the decision to add another light, or not, to your Nuvo20 will become more transparent.