All herbivores need algae in their diets. However, virtually any fish will enjoy an occasional offering of algae. If you don't have fresh algae, the next best thing is algae flakes or wafers. Algae flakes are an excellent option for community aquariums, while algae wafers are the best option for bottom feeders. Here are my top algae flake choices
1. Wardley Spirulina Plus
I’m not fond of every Wardley product, however they did a superb job developing spirulina and algae products. I’ve found their spirulina and algae flakes to be readily accepted by all fish. 
2. Formula Two
Formula Two combines algae with seafood, which makes for a highly nutritious and palatable flake food that is accepted well by any herbivorous or omnivorous fish. If you have both freshwater and saltwater tanks, this formula can be used for both environments.
3. Tetra Spirulina
Tetra foods are all quite good, and the spirulina is no exception. The only real downside is that they are pricier than other brands4. Nutra Fin Max Spirulina Flakes
Produced by Hagen, these algae flakes come in a screw top can, and are readily available at most pet shops. Although they specify Goldfish, they are ideal for any coldwater fish.5. OSI Spirulina Flakes
OSI makes a full product line of foods for Marine and Freshwater fish. They offer spirulina flakes packaged in screw top cans from a few ounces to two pounds in size.