There are many reasons why your pond has an outbreak of algae. It can be one reason or a combination of many. I have talked to many people over the past few years who are calling because their pond has algae problems. From these calls it seems there is a top potential causes which I list below.
1. New pond or major clean out.
Ponds need a balanced eco system and it can take over a year to establish this. A freshly cleaned pond or a new one contain virtually no beneficial bacteria and, without these beneficial friends, algae can break out and run amok unchallenged. Unless a pond is exceptionally dirty it maybe better to leave it alone and use a product like AQUAPLANCTON to help eat through the muck at the bottom of the pond. It can do this all year at the rate of about an inch a month. Should a clean out be essential, try doing this in early winter.
2. Too many fish
Many people call to tell me this is the first time in years that they have algae issues. They go on to say how great the pond has been and now they have 46 medium to large koi bouncing off each other in a pond that is way too small. Seems one good rule of thumb is to have one inch of fish for every ten gallons of water you have in your pond. Some say it should be closer to 25 gallons.
3. Heavy rain
Recent rainstorms can increase the nitrogen levels of your pond and make them slightly more acidic creating conditions algae love. Rain can bring in toxic chemicals such as fertilizer if the pond allows run off water to enter it.
4. Too much food (over feeding)
If you still see fish food in your pond after 3-4 minutes you may be overfeeding them and check your skimmer for excess food there.
5. Poor water circulation
Ideally you want to circulate your pond’s water every hour or at least once every two hours. Your pond may be algae free except in a few areas where circulation is poor.. Algae thrives in bright sunshine and shallow water is very susceptible to algae problems.
6. Pumps turned off
Pumps can be costly to run but turning them off can cause waterfalls to dry out and kill off all the positive bacteria you have in there plus of course vital circulation is stopped. During the warmer months when algae outbreaks are common it is best to leave the pump running all the time.
7. What else? (Other causes of pond algae)
Your pond has no shade from the sun or from any plants such as lilies. Try to provide more shade. There may be a dead fish in the pond. You have been using chemicals to kill algae or to medicate the water to prevent disease and all these can kill off the positive bacteria we are trying to encourage. Do not use insecticide or herbicide around a pond. Ducks and Geese can cause havoc to a pond as their toxic output can be overwhelming.