April 2017

One of my favorite times of the pond year is  after ice-melt in spring. The pond is brimful with water so pure that on a sunny day you can see clear to the bottom. Fish, salamanders, frogs, crayfish are all on view. Aquarium clarity like that usually lasts a few weeks until the water begins to warm up, and then a greenish shade of planktonic algae blooms in the water and pond life continues more or less in private. The loss of clarity can be mild to severe, depending on the pond, and what's going on with the weather. Drought and heat can increase loss of clarity. So can nutrients in the water and low dissolved oxygen levels. But in most ponds, a bit of cloudiness is normal, and not enough to curtail human or critter activities.

Troubled Waters

Not so last last year. 2016 was especially bad for water clarity in the northeast. A severe drought brought high water temperatures, low water levels, and lack of water exchange. Among the results, for me and many of the pond owners I worked with, was extreme loss of water clarity. Thick planktonic blooms and filamentatious algae growth made ponds unattractive and uninviting for swims. Fish kills and high E. coli bacteria levels can also result. A lot of folks got serious about water quality improvement.


There are numerous potential remedies for fighting off pea soupy ponds. Depending on the age and design of the pond, one problem can be shallow depth. Remedy: the pond may need a cleanout aimed at creating greater depth and reduced sediment/nutrient load. Also, the pond may need an increase in water supply. More water can improve depth and water volume, cool down the water, add oxygen, and increase water exchange.

But these remedies can be expensive, and risky. Pond cleanouts involve dewatering, digging, and waste removal. Care must be taken not to destroy the natural anti-seepage lining (usually a clay soil). Adding water might mean looking for more natural water supplies (springs, streams, roof runoff, etc); and ways to bring that extra water to the pond. Adding water might even mean drilling a well, although new well capacity is never a sure thing.


One water improvement option that won't break the bank is diffusion aeration. Bascially this is a bubbler system similar to your home aquarium or the fish tank at the local pet store. Except on a larger scale. Aeration systems also include surface level fountains and splashers, but in my opinion for general use the bubbler is more efficient. Essentially, a compressor pumps air into the bottom of the pond, where it is dispersed through a multi-holed diffuser, and air bubbles upward in a column through the pond, adding beneficial dissolved oxygen to the water, simultaneouly creating circulation that helps spread the oxygen throughout the pond. In larger ponds, more than one diffuser may work best. Diffuser units work best in depths 8 ft or deeper. In shallower ponds, a perforated bubbler line can be laid on the pondbed to introduce a curtain of air through the pond.

For an introduction to various aeration systems and installation specifications, check out the products offered by Kasco Marine. Next year, Kasco will celebrate 50 years in the de-icing and aeration business, developing and improving water quality systems. 

They've been a longtime underwriter for, and we thank them for their continuing support.

The results of pond aeration are multiple: getting oxygen down at the pond bottom helps decompose sediments and nutrients that might otherwise sit there using up oxygen and feeding algae growth, as well as simply building up in thickness and shallowing out the pond. The circulation also mixes up the cold and warm layers of water, which can prevent the top strata from overheating.

If you've experienced water conditions in the past that might benefit from aeration, the time to act is early in the pond season.

Waiting until mid-summer to install aeration, when temperatures are already high, oxygen is low, and algae is blooming, is not likely to be as effective as installing a system in spring. That way you help prevent trouble before it starts. But any time may be better than no time.

In general, aeration likes to begin at about 50 degrees (unless it's been running all year anyway); or early spring. The folks at Kasco suggest starting before there's any set up of thermal and/or chemical stratification. This is partially due to keeping phosphorus from forming as the result of anoxic conditions at the bottom.

At the end of the season, when algae growth tends to die back in cold water, some pond owners shut down their aeration systems. For those growing fish and wishing to maintain healthy oxygen levels, especially if fish feeding occurs, aeration may run year round. In the north, pond owners may have a couple of reasons to turn off or rearrange their aeration systems in winter. The rising column of air bubbles usually keeps an open hole in the ice, which may be tempting for animals looking for water. Animals going near these open waters may break through the ice and drown. People too. Pond owners often turn off their aeration systems in winter; or move the diffuser(s) close to shore, where the danger of breaking through is reduced.

Aeration is not without potential drawbacks. Some pond owners have found that turbulence caused by the diffuser near the pondbed can stir up mud or clay/soil particles, and cloud the water. Because diffusers are usually installed on a platform several inches above the pondbed, turbidity may be prevented. When turbidity is a problem, the platform may be installed higher (or even in a bucket). Diffusers destratify temperature layers, which is often a good thing, helping cool the upper layer in hot weather. But if you're raising cold water fish, you may not want to mix layers and lose that cold bottom layer in summer. Of course on the plus side, you're gaining oxygen down low, which fish usually appreciate. As with most things concerning ponds (plants, fish stocking, water supply, even building the pond to begin with...), it's all a balancing act, and a continuous experiment.

Photo Courtesy of Kasco Marine.

Read More Pondologies

Topics vary from month to month and provide great information when researching where you want to build a pond, or how to keep it clean.  Other areas of interest are pond use for more than swimming, and how to keep fish happy in your pond.