Controlling spirogyra/horsehair algea or any sort of algae in a pond can be a challenge if not done correctly however the proper treatment can eliminate the problem and make maintenance of a cleaner pond viable. We prefer to ensure the pond is well aerated, has proper aquatic plants to assist in nutrient removal, and is treated with beneficial bacteria to assist in the elimination of organic muck, ammonia, nitrates and other elements that can cause algae to grow.
While such algaecides as Cutrine Plus (with their 9% chelated copper) can be effective in controlling a broad range of algae including Chara, Spirogyra, Cladophora, Vaucheria, Ulothrix, Microcystis, and Oscillatoria; the problem is that using a copper based algaecide is that it can build up in the organs of certain fish and be toxic to koi, carp and goldfish.
We prefer to use non-copper products and to ensure a steady maintenance dosage of beneficial bacteria both of which are harmless to life in the pond or people and also promote a balanced pond. Using Cutrine plus or other harsh chemical algaecides can lead to a dependence. The algae grows and you will add Cutrine Plus and it kills the algae and dies and decomposes causing more nutrients and growth medium for more algae and you need to add more Cutrine Plus!
If you use a Non Copper Algaecide and then use a beneficial bacteria to assist in consuming the dead cell matter of the spirogyra/horsehair algea as it dies and sinks then you will be gradually be bringing your pond back to health. We typically start with an algaecide treatment and then after two days begin a regular bacteria treatment. The bacteria we recommend has barley-straw added which acts as a natural algaecide, this, combined with the nutrient eating natural bacteria, will keep the pond water clear.
The two step combination of non-copper algaecide and natural bacteria treatment that we use along with prices and dosage information is available here: http://www.thepondreport.com/pond-algaecide-natural-bacteria.shtml
Yes, the non-copper algaecide is safe for use in ponds where the fish are to be eaten as it basically works by oxidation, causing the algae cells to explode. It actually releases oxygen in to the pond as it is applied so is not only good at killing algae but also good at increasing O2 levels. The beneficial bacteria contains natural strains of bacteria which are also safe for fish and people and will not affect taste or lifespan of your fish. Using both products together will really help knock down algae problems and increase water clarity and reduce sediments. Just ensure to apply the correct amount of algaecide and bacteria according to the size of your pond.