At $300 you can get a WAY better light. Don't take this the wrong way, but trust my 12 years of experience (6 years with led fixtures of all kinds)... if you buy a second fixture you are doubling down on a loosing bet. Don't do it!
Adding a 2nd one of these doesn't solve the problem. Doubling the total watts isn't the issue as you double the number of leds as well. These weak leds, 0.5 watts, don't penetrate the water very deep. Oh, they light up the tank so you can see, but they don't make enough light for the zooxanthellae (algae) inside the coral to do photosynthesis that feeds the coral. Even with 2 or 3 of these over a tank of 18" or more, you seriously risk starving your coral. A 165w black box has roughly 55 leds that are rated for 3 watts and driven at 2.2 watts to keep them cool and make them last longer.
You asked for advise, I'd suggest you take it and return this fixture.
Return this or use it over a refugium to grow algae. Then spend $100 to $300 on a good fixture with 3 watt leds that penetrate the water down to 30" or more.