The normal algaecides to ...

The normal algaecides to eradicate algae from ponds is copper sulphate & chlorine. Both have very high toxicity for fish and is not advisable to use. Alternatively I recommend the use of Chlorine Dioxide as it works by oxidation and toxicity studies have shown that it is gentler on the fish. 

To start with, I recommend a dose of 1 ppm. Since the area of the Pond is 3.5 sq. mtrs. you need to know the depth of the pond as well. If the depth of the Pond is 5 mtrs then you have 22 cubic meters of water or 22,000 liters of water. A 1 ppm dose of 31% conc. product will require 70 ml of chlorine dioxide + 70 ml of Activator (15% Conc. Hydrochloric Acid). This should be added at night time so that the chlorine dioxide gets a chance to work through out the night. 

In the morning all the algae would have settled to the bottom of the pond. You can use a net to remove the algae from the bottom of the pond. 

As chlorine dioxide is biodegradable in the presence of sunlight, it breaks down into salt and water. It is for this reason that the chlorine dioxide treatment should be carried out at night time. 

Once the algae is removed from the pond a maintenance dose of 0.2-0.5 ppm should be added every night. As nutrients will always enter the water and the algal blooms will occour from time to time.