An aquarium with no background is not suitable. Lack of security can lead to stress. Some people prefer to have clean rocks and plants. In this case the algae must be removed periodically. Basically, it's a matter of preference.
Brown algae is a problem indicator.
Its presence suggests improper lighting. For algae to be green, intense light is required. The amount of water changed depends on the number, size and type of fish in the aquarium. The hobbyist will soon determine how much water to change by noting the improved behavior and appearance of the fish. By efficient, I can't emphasize strongly enough that as the water is changed, accumulated waste should be siphoned from the gravel.