Every pond owner has faced the dreaded algae bloom at one time or another while caring for his or her pond. There are several types of algae, the most common being Planktonic (green water) algae, filamentous algae and string or hair algae. Keep in mind that not all algae are bad, and some algae in your pond actually is beneficial, not only for the health of your pond, but also for the well being of your Koi.
Green water algae is just like it sounds— the water is green, like pea soup, and you cannot see your fish. String or hair algae sticks to everything; it hangs on the waterfall, on the rocks and on the stems of your water lilies. Filamentous algae is the ugliest of all the algae. Floating clumps of algae form on the surface and through the water, settling to the bottom of the pond at night.
Algae in your pond is a natural occurrence and will not harm your Koi, unless the string or filamentous algae is so thick that the fish cannot swim or so plentiful that it depletes oxygen in the water. Warmer weather promotes algae growth, but that is not the only contributing factor. Most people, without realizing it, tend to overstock and/or overfeed their fish while under filtering and under aerating, causing excess nutrients to build up, which, in turn, feeds the algae. Appropriately sized filtration, adding beneficial bacteria, proper stocking/feeding of Koi and the correct balance of plants are all key ingredients in keeping algae under control, as well as keeping your Koi healthy.
Having a filter for your pond will not do a bit of good if you are not cleaning the filter regularly, or your pump is too small for the size of your pond. Filters come in many forms, including skimmers, pressure filters, gravity-fed filters, submersed and external bio filters. It is important that your filter has both mechanical and biological filtration. Bio filtration creates surface area for good bacteria to grow, while mechanical filtration helps remove waste and muck. Mechanical filters should be rinsed and cleaned regularly to maintain efficiency. As for pump size, your pond water should be turned at least once per hour through the filter system.
Beneficial bacteria should be added to new ponds and also to established ponds during the spring and summer months to help grow good bacteria, which will compete with bad bacteria and algae for nutrients.
Nitrate filtering aquatic plants are equally important in maintaining a balanced pond. Plants will help provide shade and oxygen while they uptake the nutrients that would otherwise feed the algae. There are four categories of aquatic plants:
All plants are beneficial to your pond, but oxygenating plants will be most advantageous in helping to control green water algae. Keep in mind that submersed plants will create oxygen during the day, but will use oxygen and create carbon dioxide when the sun goes down. Basically, having too many submersed/oxygenating plants is not good for your pond.
There are two simple rules of thumb when it comes to feeding and stocking your pond. Never stock more than one inch of fish for every 10 to 20 gallons of water, and allow room for growth. Also, feed your Koi only what they can eat in three to five minutes a few times a week. There is no need to feed your Koi daily. They will do what comes naturally and will scavenge the bottom of the pond for algae, bugs and other nutrients.
Patience is key for algae control and pond clarity; there are, in fact, no true quick fixes.