I have a half acre pond about 6 feet deep and I have a algae problem, I used a gallon of Algi-cure with no success a couple weeks ago, any other ideas I can use

Be careful killing the algae at this time of the year in the whole pond. You could cause an O2 crash. I'd look into using Cutrine Plus Liquid if the algae is in the upper 24" of the water column. Read the label for application rates. If the algae is below 24" from the surface, look at Cutrine Plus granules. Some types of algae are harder to kill than others, what type do you have?

Be prepared to re-treat every few weeks if you can't mitigate the excess nutrients in the pond.