Algae problem

I'm starting a new 25gl. marine fish only tank (only 2 small damsels for
now) and going through the cycle, which is almost complete. Amonia,
nitrites and PH are all stable. In the last week out of nowhere the tank
was overrun with a brown/orange algae, which has now turned to a light
green, completly covering the crushed coral substrate and piece of synthetic
coral, but not much on the glass. I'm interested in the cause and how to
prevent it, but right now I just want to know the best product to get rid of
it.

TIA
Billy