Above ground pools can be difficult when trying to get rid of algae, only because there is no "Main drain" or a drain at the bottom of the pool which helps the filtration process greatly. An above ground pool usually only has a surface skimmer. If you've started with clean water, small amounts of chlorine should be added while filling. As far as rust being in the water, you need a metal sequestering agent which will remove the metal from the water. There are a couple of different ways to address the "green" in the pool. Since you have a sand filter, there should be a backwash mode in which the water is pumped to waste. Ideally, if your filter is equipped with a "multi-port" valve, then there should also be a "waste" setting on the valve. Brush the pool, add a floccing agent (this will drop all algae to the bottom of the pool) and then vacuum everything that has dropped to the bottom out to waste. Another option would be to brush the pool often and run the filter as much as possible. Unfortunately, sand filters have a higher micron count and take much longer to clear a green pool, especially if there is no main drain. The water would need to be continuously stirred up to be able to filter it through the surface skimmer. If all else fails, drain the pool and re-fill being sure that a metal sequestering agent is added to counteract the rust in the water.