Aviad,
Even if this product kills hair algae, the algae will die, decompose, and release the nutrients they have accumulated into their biomass back into the aquarium. To rid yourself of hair algae I would recommend controlling nitrates and phosphates. Have you considered adding a chaetomorpha / Caulerpa refugium? Running iron hydroxide phosphate removers like phosban has helped me some with my algae problems. Of course lots of water changes with RO/DI or another type of pure water will help. Are you currently using purified water to mix your saltwater and topoff with?
Kevin