Pond Aeration Tips

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Written By Mark Washburn

Mark has 20 years of experience as a professional pond management consultant.

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It may come as a surprise to learn that fish need oxygen too. Without it they, just like you and I, would die. Pond aeration, or in other words, using an aerator, is one of the best things you can do for a pond and for fish.

A pond aeration system is normally an after-thought for people who own ponds. Maybe this is because we assume that water doesn’t hold much oxygen or that fish don’t need it, but nothing could be further from the truth.

Keep in mind that what we’re talking about here is not quite the same oxygen that you and I breath out of the air. Water actually holds dissolved oxygen (DO) and it’s vital to a pond’s inhabitants and to the pond itself.

Fish Health And Dissolved Oxygen

Regardless of the species for those with fish ponds, our friends with fins are often important whether it be from the high cost of some koi, to the sentimental value of a gold fish. There’s a good bet that large pond owners have a vested stake in keeping their catfish or bass in good shape too, so every pond, no matter the size can be affected by poor oxygen concentrations.

Fish actually breath through their mouth and as water is sucked in, it’s forced to pass through the gills where oxygen is then extracted from the water. Fish actually have nostrils as well but those are only used for smelling scents, not for breathing. Fish are very capable at oxygen extraction. Water tends to hold much less oxygen (about 2 to 5% of the air we breath on land) so it’s important to be very efficient and fish pull about 85% of the available oxygen out of water.

What Creates Low Oxygen In A Pond?

Even with this capability, fish will still have problems if there is not enough oxygen available in the water. Several factors affect the oxygen holding capacity of water. For instance as the water temperature increases, and particularly as it goes above 78* F. the capacity for water to hold DO drops pretty fast. This is why very hot, prolonged summer periods can cause fish losses.

Other factors that create a DO deficit include other substances such as minerals, chemicals or other gases, may take up space that would normally be available. If plants of any kind are present in the pond, they add oxygen during the daylight hours and pull oxygen at night and periods near dawn are usually connected with the lowest levels of the day. And if they experience a die off they will pull oxygen rapidly from the water if the plants are abundant.

DO is measured in milligrams per liter and most fish will do quite well at any reading from 5mg/L and above. If the dissolved oxygen concentration get’s below this amount, fish begin to become stressed and some may die. Larger fish are particularly at risk because they require more DO to function and survive compared to smaller fish.

Why Pond Aeration Helps

Oxygen get’s into the water in several ways. First when there is agitation at the surface, either through wind, or some other “disturbance” it’s much like a barrier is being broken and an active exchange of oxygen goes into the water and other gases may go out. As mentioned plants that are going through photosynthesis also release oxygen into the water.

However plants provide a give and take when it comes to DO and there are times when the wind either doesn’t blow or the temperature get’s so hot that the water can’t hold much DO anyway. It should also be noted that unless the wind is blowing really hard, the deeper parts of a pond may still have lower DO content compared to the water at the surface.

Fish can certainly adjust their depth to find the best oxygen levels and they may even resort to gasping at the surface in very stressed conditions. Apart from this the pond’s health may suffer due to low DO levels down deep. Much of the cleaning bacteria that help to keep organics and rotting material from building up at the bottom are aerobic and this means they too require good oxygen levels to work well.

The real answer to guarding against low DO in the hot summer as well as maintaining good oxygen counts in deep water is submerged aeration. A typical aeration kit will have a land based pump (either electrical. solar, or windmill generated), an airline, and a diffuser system that sits at the bottom of the pond. This system drives air out the diffuser in a very fine bubble array that rapidly rises to the surface of the pond. This movement not only helps create a “break” at the surface to help with oxygen exchange there but it also creates a type of vortex of water movement that goes up to the surface, across the top of the pond, then back down to the bottom again. This allows a better, more widespread distribution of oxygen loaded water throughout the pond.

Many pond aeration trials have shown that fish loss can be either lessened greatly or eliminated entirely with adequate aeration.

Pond aeration systems are all similar in how they work. Most kits are rated in terms of the pond size and depth they they will work best at and to get the best results it’s suggested to consult the manufacturers recommendations on a particular system.

Costs will vary but most small pond systems are quite affordable and range from about $50 up to $500 while large pond systems can range from $600 or $700 up to several thousand dollars. Operational costs are relative to the size of the system but are generally affordable for most pond owners.

All Season Aeration

It may seem that the warm summer months are the best time to use aeration and while that’s true, there are also benefits of using pond aeration in the winter as well. In moderate climates an aerator alone may help keep the pond’s surface free of ice and at the very least it’s a good idea to keep a section of ice open even in the coldest conditions. Large waters benefit here too and the most effective tool for this work will be an aerator package.

Consideration should be given to the placement of the diffuser sitting at the bottom of the pond. In the summer it’s suggested to put the diffuser in the deepest part of the pond to allow full oxygenation and circulation. In winter, the diffuser should be moved to shallow water, not only for it to keep a hole open in the ice but also to allow the fish to go to deeper water and be undisturbed. Normally in winter, deeper water is warmer.

It’s unfortunate that many fish pond owners don’t make the move to add aeration to their pond until or after they’ve experienced some fish losses. It’s a hard way to learn a lesson but the promise of a healthier pond and fish can be the result after adding a good pond aeration system.

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