wait until your tank has fully cycled (ammonia = 0, nitrites = 0). by the sound of your numbers, this could take about 2-3 more weeks at least. then perform a 20% water change to reduce your high nitrates. it may take a while for the nitrates to come down...you may have to do a series of 10-15% changes.
to keep your algae under control, don't run your lights at all during the next few weeks. also, make sure your tank isn't receiving any sunlight as this will lead to algal blooms. running your skimmer (if you have one) is fine during the remaining few weeks of your cycle.
depending on your tank size, once the cycle is complete, add a cleanup crew. nassarius snails are best, along with some hermit crabs.