Algae are considered the biggest problem in a pond. In reality Algae is your best friend. The real culprit is that residue on the bottom of your pond.
Bottom waste is comprised of fish waste, snail waste, dead leaves, and plant material, dirt out of the air, and any solids from drainage into the pond. This material forms a bacterium that breaks down into gasses, ammonia and other forms of fertilizer.
This fertilizer must be consumed. The fastest consumer of this fertilizer is algae. If the bottom waste is so rich that the grasses and water lilies cannot consume it fast enough, then hair algae is a result. Again if the bottom material is so rich that the hair algae cannot function properly, then the free-floating algae or green water is the end result.
You can drain your pond every day forever, but as long as that bottom two inches remains, there is a problem.
A certain amount of bottom material is healthy for a fish pond. Monthly vacuuming of about 70% of the bottom material is usually about perfect. Vacuuming more often only disturbs your pond unnecessarily.
When operating a pond sweep, move forward one foot, and then lift up approximately two inches (as shown above) to allow the dirt to be vacuumed through the sweep.
Helpful hint; using Uber-Tech Water Restore 3 to 4 months before sweeping your pond will yield maximum results.