Nobody is happy when their pond water turns green, or when hideous masses of thick, green strings of algae erupt from the liner, ornaments and every other surface in your display. You work so hard to keep your pond clean, clear and looking good, but even with the best efforts, algae can appear in a flash, a stringy, slimy eyesore mucking up the view. Algae outbreaks may be fixed by addressing water chemistry issues such as presence of phosphates, high nitrates or other organic nutrients and by limiting the amount of sun exposure the pond gets in a day. While these underlying causes should certainly be addressed to eradicate and prevent algae outbreaks from beginning, there are numerous products for pond algae control (both natural and engineered) on today's market to help you rid your pond of that unsightly green invader in the meantime. While we generally recommend algaecides as a last resort, when you reach that point it's important to use them correctly to ensure the safety of fish, plants and other inhabitants of your pond.
The first thing to know when applying any treatment is the size (volume) of your pond. Overdosing, particularly with chemical algaecides, can be lethal to pond animals and plants. Calculate the volume of your pond with these formulas: Rectangular ponds - Length x Width x Average Depth x 7.5 or for round ponds - Width x Depth x 70.5. Make sure that all of your measurements are in feet. For oddly-shaped or angular ponds calculate using the surface area x the average depth. Once you know how much water you have to treat, you'll be on the way to successful algae defeat.
Next you'll want to explore the various types of algaecides and algae-fighting treatments available to find one that will suit your needs. What kind of algae are you fighting? Do you have livestock in your pond, or do pets and other animals drink from the pond? Do you have ornamental plants in the pond that may be affected by the treatment you use?
Natural solutions including barley straw products, biological additives and fish safe water dyes may be the first options to explore. As the lignin in barley straw biodegrades, natural compounds act as oxidizers to combat algae. Barley pellets, extract and other variations work the same way, but faster, as the compounds are more readily available in these forms. Biological additives boost bacterial that help to digest muck in the pond, reducing nutrients that feed algae. Water dyes and tints block the sunlight and prevent algae from forming and taking over. These methods allow for continuous control, simply replenish the straw as it degrades and the dye as it fades to keep algae in check.
For larger problems including ponds already overwhelmed with algae, free-floating algae blooms or algae on tough to reach or clean surfaces like rocks and equipment, stronger algaecides or other equipment may be necessary. Algaecides for planted ponds are generally formulated with oxidizing ingredients that destroy algae on contact or chemical ingredients that break down cell walls of simple alga. These treatments are typically safe for fish, ornamental plants and other animals in and near the pond provided instructions are followed. Algaecides for non-planted ponds often contain copper as the active ingredient which has the potential not only to kill plants, but is also harmful to snails and other organisms in the pond. If you have an advanced free-floating algae issue (if your water is green like pea soup) you may consider adding a UV sterilizer unit to your pond to clarify and prevent future blooms. While the initial cost may be more than the cost of an algaecide treatment, free floating algae will usually reoccur, and a sterilizer can be a permanent solution.
Manual removal of as much algae as possible before treatment is highly recommended to allow algaecides to work more efficiently and to prevent mucking up the pond after treatment. Closely follow the manufacturer’s instructions to ensure proper dosage and to take any precautions in using chemical means to keep your livestock safe during and after treatment. Make sure you have adequate aeration and surface agitation to supply your fish with vital oxygen, especially important during the warmer months. CO2 build-up and the new absence of oxygen-producing algae can cause an instant drop in available dissolved oxygen, especially if you treat in the evening. Low oxygen levels may cause fish to become sluggish or listless, and you may see them gasp at the surface or congregate at a fountain head or waterfall where more oxygen is available. If ample aeration is not restored, your fish may not survive. It is best to treat early in the day when you are able to observe how your animals are responding and take steps if necessary to add more aeration should they show distress.
Remove as much of the dead algae and debris as possible when treatment is complete, so that it isn't left to decay in the pond. Once treatment is finished, a partial water change/siphon is also recommended, with particular attention to the bottom of the pond to remove the debris that may settle there. Addition of a biological "sludge remover" or bacterial supplements will help to breakdown the remaining debris to prevent water chemistry issues.