Welcome.
That light is huge, and will probably always need to be very dimmed. Also, I don't know how well they handle salt spray.
The screen is 1-sided, which is much less efficient than 2-sided for the same size.
You could just let it run, since it's already built. If you want to improve it, you could put a reflector or white on the other side, and put a 2" open gap down the middle of the screen (making 2 separate screens), and seal up the middle of the slot. Light will go through the gap and reflect off the other side to partially light the other side.
Best would be to get a light on the other side. But in your case it would be a big rebuild, so you might as well see how it grows now.