Karen,
Like others have said, the water at that place when we tested it was just plain terrible. All your algae problems are stemming from your source water and any supplements or additives would simply be a waste of money. Look into the RO/DI units that Gabriel is recommending or at the least, get some 5 gallon jugs from Walmart and fill them at your LFS of choice. RO/DI water usually runs between $.20-$.25 a gallon and with a few water changes and time, your algae problem should dissapear.
Good luck and at least you have a definitive source for your problem algae!
John