Is this a brand new tank you are setting up? If it's just a bit of hair algae I wouldn't worry about it. Proper care of the tank and certain animals will eliminate it. Expect to have some algae at the start of a new tank anyway.
The green algae in your pictures is Halimeda algae. It is calcerous and is considered good to have as it is not evasive or competative. It is also usually a good indicator that your tank is doing good as it dies quickly with ailing water parameters.
The snail, brittle stars, etc you have don't require any light so if you want to turn the lights off for a few days it won't hurt them. They are actually more active with the lights off.
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