RE: Green Algae Question
Light does not cause an algae bloom, nutrients do, especially phosphates. Without nutrients you can have as much light as possible and you won't get an algae bloom. Is light necessary for algal growth? Yes, of course. Is the solution to starve the tank for light, no! The coraline will be hurt just as much as the green algae.
I would suggest frequent, large water changes while its cycling and if possible, using a phosphate remover such as phosban or phosguard. I realize you are very limited in what you can do for filtration in a tank that size. Its one reason why nanos and picos are very difficult tanks to manage.
With a tank that size its relatively easy to simply remove the rock and clean it with a toothbrush if the algae gets to be so bad that you think it might choke out the coraline.
Gary
125 SPS, 75 gal. LPS/softie reef, 9 gal. Nano