Fins, here is a recommendation from someone who treats ponds on a regular basis in the state of Ohio. I use Cutrine Plus in the liquid form 99% of the time. In regards to algae, there are many different types and you don't have to be an expert to treat them.
When treating with Cutrine, mix 3 parts water to 1 part Cutrine and spray directly on the Algae. If you have any problems with the algae not dying or not getting the control you want you can us another chemical with it. It is call Reward and it can be mixed with the Cutrine at a 0.5 part. So ex. mix 3 qt. of water + 1 qt. of Cutrine + 0.5 qt. of Reward.
With that being said, you should be using Grass Carp and a bottom based diffused aeration system. I am amazed at how many people don't have Grass Carp stocked in their pond. They do an excellent job once your water starts warming up. Don't get me wrong they are not miracle workers. They are typically good for about 5 years. So make sure you are restocking them periodically.
For the record, if any professional recommends using barley to kill algae, they can be fined big time! It is not for farm ponds! Water garden ponds fine......
