Aeration of Large Ponds
This section is for those with large ponds.
Though aeration occurs naturally in ponds, additional pond aeration is often necessary. A proper pond aerator is necessary to insure the health of your fish and the entire pond ecosystem. But what kind of system is right for your pond depends a lot on the pond’s average depth and what it is you want your pond to accomplish.
Lack of aeration causes your pond to stratify, form layers in the water; typically these layers are different temperatures with different levels of oxygen. The top of the pond can become stagnant and full of muck. Also, muck will accumulate at the bottom of the pond unless there is proper aeration, and it will become shallower over time. Plants in your pond, including algae, need oxygen to decompose. And if they don’t get enough oxygen, the old plants will decompose faster than the new ones, sending up noxious gas bubbles from the bottom. A pond aerator system will de-stratify your pond and result in less chance of a fish kill and bad forms of algae and other noxious weeds.
You don't want your pond looking like this photo. Pond Scum Image
Fish Kill Image
Common Ways to Aerate
Basically, there are two different ways to aerate, from the top of the water and from the bottom. Whether to get a surface aerator or a bottom aerator or both depends on your pond depth and the overall goals for your pond.
Aerating from the surface is the most common. A float sits on your pond, usually black to blend in the water, and a pump is attached to the underside of the float. The float allows the whole unit to rise and fall with the water levels. But what kind of water flow and thus aeration you get depends on which kind of surface aeration you choose.
Decorative Surface Aeration
The most common type of surface aeration is the use of a decorative fountain. A nozzle sits on the float attached to the pump. The display can be quite dramatic and complex with several angled holes--or be simple. A decorative fountain pump will use an impeller. The idea of a decorative fountain is to focus on decoration first and aeration secondarily. Kasco Marine recommends a 2 to 1 ratio: for every surface acre of pond, use 2HP of decorative fountain. And Kasco concentrates on aeration for ALL of their fountains. For some other brands, we would recommend up to 5HP of fountain for each acre to be aerated. Fountains that push the water high into the air and wide typically do so my shrinking the size of holes in the nozzle. Thus, with these kinds of fountains, aeration is decreased.
Aerating Fountain Aeration
V-shaped aerating fountain
An aerating fountain will provide more aeration than a decorative pond fountain. Instead of an impeller the pump will use a propeller. Also, the “nozzle” is basically a large hole, which provides only the V-shaped pattern. Kasco recommends a 1.5 to 1 ratio. 1.5 HP pump for every surface acre of pond.
Plain Surface Aerators
A solar surface aerator
There is one other kind of surface aerator, and this one provides the most aeration of all, probably double of what a decorative fountain will do. A propeller is used for surface aerators, too, but there is no nozzle at all, and thus no restriction to water output. There is also little display, just large splashing bubbles. Kasco Marine recommends a 1 to 1 ratio for surface aerators.
Bottom Aeration Using Diffusers
The thing is, if your pond is deep, with an average of over 7 feet, bottom aeration works best. An air compressor is located at the shore and a hose carries the air to a diffuser unit at the bottom of the pond. Though compressors used to be rather loud, nowadays they are much quieter. They are also very energy-efficient, and a great deal of aeration can be done with a quarter horsepower compressor. They need to be housed to protect from the elements, thus quieting them more. If your pond is shaped conventionally, as a rectangle or oval, then it’s often the case you will only need a single diffuser at the bottom of the pond. If it has islands or unusual shapes, there’s a good chance you will need to place more than one diffuser at the bottom.
We really think the Kasco pond aerator system is the best bottom aeration on the market.
Combining the Two Kinds of Aeration
If you have a deep pond but still want to see a fountain, you can combine the two types of aerators. A pond aerator system could use a surface fountain for display and agitation of water below, and the diffuser system would properly increase dissolved oxygen levels. The fountain would not need to aerate as much and could focus on beauty. This focus allows for a greater range of price as well as dramatic viewpoint.
You can add lights to any of the surface aerators, even pure aerators.
Aeration for Small, Backyard Ponds
This section is for aerating those with small, backyard ponds, usually with koi. Even in small ponds, fish and the pond ecosystem need oxygen year-round. Oxygen can be added to the water in several ways.
Waterfall and Streams
My personal favorite has always been the waterfall and stream combination. These keep the water moving and reduce stagnation, all the while adding oxygen to the water. They also are terrifically easy to build, much easier than making the pond. Building a pond necessitates a lot of digging, leveling, and placement of boulders or flagstone around the edges.
But the extra dirt you have from digging the pond can be used to build a waterfall! First you make your mound, which can be quite short or really tall, depending on how much height you want. Remember, taller spillways do make more sound, but at the same time they can cause more splash, potentially leaking outside the pond. It is best to use some large boulders around the spillway to decrease the splash outside of the pond.
Spillways can be made with flagstone, which is easy to break into smaller parts, or you can buy acrylic spillways to fit between boulders.
You will need to decide how many spillways you want. Is it a one-tier waterfall, two-tier, or even more?
Once you’ve created the shape of your waterfall, you really should place liner and underlayment below the liner. It is tempting to use concrete, but it almost always cracks. You can always cover the liner with concrete if you prefer a concrete look.
Try to choose rocks of various colors and texture. Rearrange them until you find the right look. You can also add driftwood or other ornamentation.
A stream can be formed simply by trenching a shallow ditch going to your waterfall. Again, cover with liner and underlayment. Streams are often prettier if small stones, like Mexican pebble, cover the liner.
Small pond fountains also will aerate the pond, but remember to constantly keep wind in mind. Nozzles with tiny holes in them will often plug up and the water droplets can be so light that the water can easily drift outside of your pond.
Carefully adding plants will also not only beautify your pond but also add to oxygen levels and provide shade for koi.
Another way to add oxygen to your pond is by placing a diffuser in it. A small compressor is located outside the pond and tubing is connected to it and connected to a diffuser that sits on the bottom of your pond. The diffuser will have a number of holes in it out of which columns of air bubbles rise to the pond’s surface.
Ponds NEED oxygen to sustain a healthy balance. There are several ways to aerate your pond, which will help your fish and the entire pond ecosystem. And remember, do NOT add more fish than the size of your pond can handle.
Don't forget the aesthetic value of lights!