a FR helps to increase the contact surface of the phosphate removal such as ROwaphos and phosguard, thus increase the efficiency and value of the product u buy. minimum wastage .
is FR a must , IMO , i dun think so , there are product like ROWAsponge which help to remove phosphate too , although some claimed it is not as effective as ROWAphos itself .
look into like ur flow and ur lighting in the tank can help to lessen the algae problem.
generally nitrate and phosphate are fertilizer for algae