If you have a pond, you likely have fish in it for you to enjoy and to help create a healthy ecosystem. It’s also likely that you have algae that grow incessantly and give you a headache. Algae are normal in a standing body of water, and although a small amount is natural and beneficial, once they become excessive something needs to be done.
When algae are overgrown, they can cause low turbidity in the water which allows particles to stay floating. This prevents water movement, which creates more algae growth. Some algae, referred to as cyanobacteria, can even release harmful gasses into the water and the air around your pond when they are left to bloom unchecked, harming you, the fish, and other pond wildlife. Thankfully, there are plenty of ways to remove algae and prevent its regrowth without causing harm to the fish that live in the pond.
Read on to educate yourself and decide which of these solutions will best benefit you and your situation.
Physical or Machine Solutions
Many people, especially if they have small ponds, choose to manually remove algae with a tool. Pond rakes or nets can dig up much of the algae around the sides and bottom of a pond, especially if there is not a ton present. However, if the pond is quite large or if there is already significant overgrowth, then a larger raking machine will probably be a better bet.
These rakes or nets (manual or machine-powered) also don’t pull up algae by the roots, so it will continue to return unless you add in other preventative measures.
You could also add an ultraviolet (UV) light clarifier, which emits very high levels of UV light that don’t promote growth but inhibit it. The levels of UV light that these clarifiers emit destroy algae’s ability to reproduce.
Fish are not harmed by rakes and machines, as they can feel the motion vibration and swim away. However, remember that algae are plants, which provide oxygen, and fish need oxygen in the water for a healthy environment. So, if you are removing much or all of the algae, it is a good idea to make sure some healthy plants are still present in the pond.
Another great way to prevent algae growth is to keep the water moving by adding in an aerator or fountain, depending on the size of your pond. Moving water and highly-oxygenated water keep algae from producing in excessive amounts.
Non-Toxic Chemical Solutions
There are a few different chemical solutions that one can use in a pond that will remove algae without harming fish. You are ultimately responsible, though, for making sure that the fish that live in your pond will tolerate what you are using and that the pH level of the water, the species of fish, and the chemical will all tolerate each other.
Many people like the simple solution of dying their pond water. If you dye the water a darker color, it will absorb less light. High-intensity or bright light is a catalyst for algae growth, so once you initially remove algae (with a rake, machine, or decomposer), dyed water will be less of a suitable host for more algae regrowth.
One of the best algaecides out there that is safe for fish is a peroxyhydrate granular algaecide (which comes under many brand names). This comes in a solid granule form, and when added to pond water, it oxidizes, which destroys algae growth! This is a quick, easy solution that will start to show results in just a day or two.
Animal or Plant Solutions
If you are trying to keep things as natural as possible, using an animal- or plant-based solution is a great way to remove algae from your pond.
One of the best, easiest, and most beautiful ways to remove and prevent algae growth is to add floating, oxygenating plants such as lilies or lotuses. Floating plants are a great way to provide shade on your pond’s surface and prevent a great deal of direct sunlight from entering the water. They also absorb nutrients themselves, taking them away from the algae, thus, starving them.
Carp is a species of fish that will eat filamentous algae, but they do prefer weeds. Adding carp is a good solution for removing algae if that is the main weed growing in your pond. In most places, carp are invasive, though, so they will need to be proven sterile before adding them to your pond.
Barley straw is another plant product that destroys algae growth. This solution takes time, but it is completely harmless to fish and uses no chemicals. You place the barley straw in the water and it decomposes over a few months, depending on the temperature of the pond water and how oxygenated it is. The process is a bit complicated, but when the barley straw breaks down, fungi in the water will eat the remains and produce something called humic acid, which reacts with water and sunlight to eventually produce hydrogen peroxide, which, in small amounts is very powerful at killing algae while still being safe for fish.
For the fish that are already present, make sure that you are feeding them high-quality fish food that they will be able to digest at the highest level possible. If they are not digesting a great deal of their food, then those lost nutrients will go into the water and be available for the algae to use instead. So, the more nutrients that go into the actual fish (which you want to thrive) the better.
Ultimately, the decision of how you remove algae from your pond and keep it from coming back in harmful amounts is up to you. You will need to weigh all the deciding factors, such as if your pond is natural or man-made, the size and shape, and what type of wildlife are present in and around the water. Hopefully, this has given you a range of solutions so you can find the best one for you.