Pond Algae: Green Pond Blues
Pond algae are pretty easy to control. If you have koi, you must have an extensive filtration system to control algae. If you have goldfish and feed them, you must have filtration, but you can control algae. If you do not feed your goldfish and do balance your pond, algae rarely grow at all.
When sun hits water, algae grow. That is the way of nature. In order to break that cycle, there are things you can do easily to keep your pond water clear and healthy. Most of the following suggestions are germane only if you have goldfish and do not feed them. I have included a few for you goldfish feeders who simply cannot help yourselves.
Balance your pond ecologically. Use bog plants like irises or umbrella plants. You must have oxygenators or submerged plants. The best is anacharis, followed by cabomba and hornwort. You must have one bunch of these submerged plants per square foot of pond surface. These plants arrive with a rubber band holding them together. Remove the rubber band before you put the plants in your pond. If you don't want them floating freely, you may pot them up in several pots that sit on the bottom of your pond. The submerged plants are fertilized by fish waste and CO2, a fish byproduct. The fish eat the submerged plants, but they grow faster they the fish can eat them. Nice cycle, huh? Nature takes care of itself if we can just leave her alone. If you have too many fish, they will eat all your submerged plants and you have to start over again. A good rule for fish load is 1 linear foot of fish per 25 square feet of pond surface area; tails don't count. If your pond gets green, have patience. It will fix itself
When pH gets on the basic side algae flourishes. Vinegar is weak and it takes forever (days) to neutralize. But it takes an expert to use muriatic acid properly, so do not put concentrated muriatic acid in your pond to balance pH unless you know what you are doing. You can buy commercial products, usually called pH down or some such. They are expensive, but work well.
It is good to have algae slime on the sides of your pond... this is a sign of a healthy pond and can generate up to 70% of the oxygen needed for your pond.
If you feed your fish, these simple ways of keeping your pond clear will not work. You will need a filter, preferably a biofilter.
You must cover at least one half the top of the pond with floating plants. Parrots feather is great, as are water hyacinths, water lettuce and water lilies. If you live in the tropics, you can have beautiful tropical water lilies. You must be willing to either sacrifice them in the winter or store them away until warmer weather arrives again in the spring.
Scotch Barley bales work, but the pond must be cleared of algae first and it takes some time to work, sometimes up to a month. Always put another barley bale in your pond before the last one is gone.
Black dye works really well in a formal or reflecting pond. The black water sets off the water lilies and they look wonderful. Anacharis can live in the black water. Do not use the blue or green dyes. Trust me they are ugly.
There are several products on the market that will wipe out algae population without harming fish or desirable plants. The downside is they kill all the algae. It clumps up in the bottom of the pond. This can cause oxygen depletion and your pond can become anaerobic. I never use any chemicals to kill algae. There is too much chance that other living things will also die. Being an organic gardener, I use nothing that has ëcide in the name. I will not introduce any poisons into our soil or water. We have too many already.
Change 25 or 30% of your pond water weekly. Pump it into your veggie or flower beds. They will thank you. When you refill the pond, don't forget the dechlor.
UV lights will work and are good when you have too many fish. They can also kill many beneficial bacteria and you are back to your anaerobic pond. Using plants to keep your pond clear and clean is certainly the easiest and best way. And it needs little maintenance.