Pond Boss Forums AERATION Should I aerate? Oxygen depletion

The following is an article in the local paper that may be of interest.

July 1, 2002

Oxygen loss in ponds can cause fish die-off

Each year, a number of pond owners experience a partial or total loss of the farm pond fish population due to an oxygen depletion. Oxygen depletion is not the only cause for a fish die-off but it is the most common.

Pond owners should be aware of the causes, signs and corrective measures to lessen the likelihood of experiencing an oxygen depletion.

Several factors may contribute to an oxygen depletion, some of which cannot be controlled by the pond owner.

The most common factors which contribute to oxygen depletion follow:

• Season - Oxygen depletion is most likely to occur in warm weather, usually June to Sept. Warm water holds less oxygen than cool water.

In addition, fish experience a faster metabolic rate as water temperatures increase, which means a greater requirement for oxygen.

This increased requirement of oxygen, at a time when it is less available, increases stress in the fish population.

• Weather Conditions - Sunlight is necessary for phytoplankton to produce oxygen through photosynthesis.

Several cloudy days in a row limits photosynthesis resulting in less oxygen produced. Cloud cover along with hot, still weather worsens conditions.

Oxygen demand by fish and plants may exceed the rate of oxygen production, thus creating an oxygen depletion.

Another weather condition conducive to oxygen depletion is cold wind and/or rain during the summer.

Usually, ponds are stratified during the summer season with a warm layer of water near the surface and a cooler layer on the bottom.

Cold wind and/or rain causes these two layers to mix rapidly, resulting in the breakdown of organic material present on the bottom which is evidenced by a foul, musty smell.

This process removes oxygen that is normally available for fish to utilize and it is a process that is commonly referred to as a pond turning over.

• Exceeding Carrying Cap-acity - This simply means too many fish in too little water.

A good rule of thumb is to never exceed 1000 pounds of fish per surface acre of water during warm weather.

• Improper Aquatic Weed Control - Most pond owners wait until aquatic weeds become too mature and dense before they decide to use an aquatic herbicide.

Herbicides should be used when new growth begins in the spring.

Best control is obtained at this time compared to treating once plants mature.

Treated plants sink to the bottom to decay and this decomposition process removes oxygen which is already at a marginal level during hot weather.

If a heavy enough growth of weeds is killed in a single application during hot weather, oxygen depletion is likely to occur.

A pond that must be treated in late summer should be treated in three or four different sections, some seven to ten days apart.

Select herbicides formulated for sectional or spot treatment as mentioned on the label.

Never use a herbicide that does not have an aquatic use label as this may further complicate matters.

• Overfeeding/Over Fert-ilization - Occasionally ponds become too rich due to an over abundance of nutrients.

Sources of nutrients include waste products from the fish, decaying uneaten feed and over fertilization.

A deep green or blue-green water color may develop as a result. Feed fish 3 percent of their body weight per feeding.

If this cannot be calculated, feed what they will clean up in 15 minutes (not to exceed 15-18 pounds of feed per surface acre). A floating ration is best for observing fish during feeding.

A fertilizer that is high in nitrogen and phosphorus, such as a 20-20-5, should be applied at the rate of 100 pounds per surface acre in the spring once water temperature reaches 65 degrees F, followed by 50 pound applications at 30 day intervals until the water temperature drops to 70 degrees F in the fall.

More or less fertilizer may be required depending on plankton bloom.

Small ponds managed intensively for catfish are the most susceptible to oxygen depletions, but larger sport fish ponds are not exempt.

If fish appear at or near the surface and swim sluggishly, this may be a sign that oxygen depletion is occurring.

Oxygen is normally at its lowest level at daylight, therefore pond owners are advised to observe fish early in the morning.

A change in water color from a greenish hue to a brown or coffee color may also signal an oxygen loss due to a phytoplankton die-off.

Aeration of the pond to increase oxygen content is the best technique for relieving an oxygen depletion.

To increase oxygen levels, pond water must be brought in contact with air.

Pulling water from near the surface and spraying it back over the pond will increase oxygen content.

Outboard motors can also help increase oxygen levels by running in a fixed position.

The idea with a pump or motor is to create a pronounced circulation pattern in the pond.

These corrective measures are usually only temporary and help little if the cause of oxygen depletion is not corrected.

While some causes may not be controlled, others may be controlled according to pond owner management decisions.

An awareness of the causes, signs and corrective measures of oxygen depletion allows the pond owner an opportunity to reduce the risks of fish losses.

• C. Jack Hunter is a Texas Cooperative Extension agent in Brazos County specializing in agriculture and natural resources.

Good article Bill, thanks for sharing it. I run my compressor 24/7 it is a small one and feeds 25 feet of garden soaker hose. The fish have been happy all summer and the cats have put on 8 inches or so along with several bluegill spawns.

Bill; Good article. I wonder why he says take water near the surface and spray it into the air. If the top area already contains most or more of the oxygen, I would think that he had it backwards.

Bob, A garden soaker hose sounds like a great idea if you have enough cfm to utilize all of it. Evidently you do.

Looks like a good article.

It is recommended that you pull water from the surface because it does have most of the oxygen. Maintaining a thin, oxygen-rich layer is easier in an emergency situation than aerating the whole lake. Pulling anoxic water from the bottom of the pond may actually make things worse.

Now, if you're aerating for the long term, and you don't have a problem, pulling water from the bottom of your lake makes good sense.

I unfortunately lost my fish several years ago - lost 7-8 lb bass and 15 lb catfish - only fish left alive were small perch and a few small bass - it is quite a blow if a die off strikes your pond. Mine was in late September, lots of heat and drought conditions where the pond water level had dropped. A cool rain hit one night, filled the pond up quickly and turned over all of the dead grass, weeds, etc. from the drought. Arrived next morning to finds hundreds of my fish either dead or gasping for oxygen. Thought at first they were poisioned but not the case - In most ponds aeration can potentially save much money and years of effort - starting over from scratch is no fun.

Aeration Start-Up Note: Keep in mind that if you start or begin a bottom, air injected, aeration system in early summer thru fall, only run it a short time the first day. Second day the run time can double, third day it can run triple the time, etc. Do not bring up all the bad water from the deep area all at once (continuious run) or you will degrade the upper water oxygen concentration enough to stress or even kill your fish.
Also the deoxygenated deep water usually has hydrogen sulfide (gas) in it and it is highly poisionous to fish in relatively low concentrations. The hydrogen sulfide gas is responsible for most of the bad smell during a turn over. You do not have to do this slow run time at start up if you begin aerating right away in the spring when the deep water still has oxygen in it.
PS the soaker hose can work great as a bottom diffuser BUT it plugs up quicker than many of the other membrane style diffusers. All compressors should have a pressure guage (low psi style) to monitor the pressure of the system and increased running pressure will indicate the degree of diffuser clogging.
B. Cody