It is possible with mechanical filtration to strain out the large string algae, though the smaller algae does not usually get caught by the filtration media. The best success is usually had with poly-fill natural fiber media or foam rubber and, given the minuteness, needs to be changed often, sometimes hourly in a pond that has large amounts of algae. Biological filtration, while beneficial and practical for pondkeeping, has virtually no effect on algae, except to increase it. The end product is more dissolved nutrients in the water that end up feeding the algae. Biological filtration is necessary in a heavily stocked pond, but the pondkeeper should remember that it will not aid in preventing algal blooms.
Many hobbyist utilize ultra violet filtration.
We have found that the expense is prohibitive for our needs, added to the initial cost of the unit, the cost of replacement bulbs and the fact that you must have algae to begin with, we opt for the less expensive way of dealing with algae by proper stocking of plants and fish and the proper feeding regimen of both. UV sterilization can make algal blooms worse by sending the dead algae back to the pond to feed a new algae bloom by releasing nutrients into the water as it decays. There are many chemicals out there that are advertised to help with algae problems. According to the United States EPA, no product can make algicidal claims unless the manufacturer submits data proving the product works. Once approved, the product is issued a federal registration number.