The first thing to do is remove excess debris, use a pool skimmer or make a skimmer yourself by stretching an old pair a pantyhose over a wire clothes hanger. If the pond is really bad you should empty the pond and then clean, but do this no more than once per year by removing fish etc and draining the water for a thorough cleaning.
Be sure to use a de-chlorinating agent for the water in the bucket or wading pool you’ll be using as a holding tank for the fish while cleaning (use 50:50 fresh water and pond water). Remove silt and debris from the bottom of the pond (it makes good fertilizer). If you have plants remove and place in a shady area so they do not dry out. Use a brush to scrape down the sides. When refilling the pond pour half of the holding tank water in the pond to inoculate the pond with healthy bacteria for the fish, fill the pond and be sure to use a de-chlorinating agent.
Reintroduce the fish slowly by filling the fish holding tank with water of the same temperature as the water in the pond. Pour in half of the water from fish holding container into the pond, and then re-fill the holding container, and once it is full again, empty another 50% into the pond. Repeat this process to slowly change the water temperature, until the fish pond is full again.
Be sure to also clean the filtration system, this is best done by rinsing with water as any soap residue will harm the fish. Removed much of the pond water before trying to net the fish, as it will be easier than trying to catch them with the water full. You shouldn’t clean your pond more than one per year since it take time for the beneficial bacteria to build up. If you want to clean without going to the extreme of empting the pond then use a rake and pull the debris and scoop it out, but be gentle so you don’t stir up the pond to badly.
The easiest way to keep the algae down maybe to increase the scavengers in the pond and regular skimming of the pond to remove leaves etc. Snails, mussels and tadpoles all remove the wastes created by plants and fish inhibiting the growth of algae. A good rule of thumb is one scavenger per square foot of surface.
A trickling fountain is a serene addition to any backyard, until white or green discoloration gets your blood pressure up.
Scale, the white mineral deposits caused by hard water, and algae are the main issues when it comes to fountains. Sticking to a cleaning routine will help prevent either from taking hold.
Both scale and algae build up over time. The more you prevent their buildup, the easier it will be clean your fountain. To prevent algae, use a commercial algae treatment, available at water-garden and fountain suppliers. Typically applied a few drops at a time once a month or so, these inhibit algae growth without the use of chlorine or other harsh chemicals. You can buy a similar commercial treatment for inhibiting scale,. It works the same way to keep scale from forming on your fountain, fountainhead, and filters. You use 2 to 4 ounces for each 10 gallons of water. If you want to not use the commercial products, clean your fountain as needed, usually once a week. For scale and algae, vinegar is one of the best cleaning agents you can use. Empty the fountain and, using a one-to-one solution of vinegar and water, scrub the surfaces with a nylon brush. The vinegar will neutralize alkaline mineral deposits, plus it has good cleaning qualities. Rinse well by spraying the fountain with the garden hose.
Clean the pump and filter weekly as well. Remove the filter and spray it with the garden hose. If not, algae, especially the filament shaped kind, can clog it. Wipe down the exterior of the pump with a wet cloth.
If the pump has mineral deposits, wipe it down with the vinegar solution and rinse with clean water. If you need to scrape algae or mineral deposits out of the intake valve, use the bottle brush supplied with your pump kit, or use a wooden stick, like a Popsicle stick. Metal can scratch the surface.
Caution: To avoid the risk of shock, always unplug your pump before cleaning it.