The First Call Of The Season

dead fish

It always comes, and I hate it.  It’s that first call of the season each spring or summer when the temps start to rise.  It usually goes something like this.  “Hi, I need some help here, my fish are coming to the surface of the water and appear to be gasping at the air.  Some are dying and I need to try to save the other one’s.  What can I do?”

My first response is usually with a simple question.  “Do you have aeration in the pond?”  And usually the answer is…no.

In fact I can’t think of an instance, although that’s not to say it couldn’t happen, but I can’t remember anyone ever following that question with a “yes”.  

And therein lies the problem.

Without a pond aerator in place before the problem starts, you’re going to end up in crisis mode, trying to respond like a M.A.S.H. unit in a war zone.

To start with, I’ll cover what you might try to help curb the losses in the short term.  And then I’ll tell you how to end this tragic problem for good.

Temperature Matters

In the most recent case of oxygen deprivation in a pond, the body of water was around 1/4 acre in size and the fish involved included some bass, crappie, and catfish.  This particular farm pond was in Texas, and the weather there had started to heat up pretty good with air temperatures in the high 80’s.

You might recall our past discussion on the fact that as the water temperature rises, and goes above 78 degrees, the water simply can’t hold or retain as much dissolved oxygen as it will in cooler temperatures.  So you might not see any kind of problem during the cooler times of the year, but as things heat up, everything can change pretty fast.

What’s Considered Low In Terms Of Oxygen?

DO, or dissolved oxygen can be measured in ponds with special meters.  Dissolved oxygen concentrations below 3 ppm can stress most warmwater species of fish and concentrations below 2 ppm will kill some species. Often fish that have been stressed by dissolved oxygen concentrations in the range of 2 or 3 ppm will become susceptible to disease as well.

One of the problems with this unseen element of pond water however is that you can’t really tell something’s wrong until the fish share their distress with you.  The gasping at the surface is a tell-tale sign, and in small  ponds you might find them hanging under the waterfall area, or anywhere that DO might be a little higher. (I should note too that if you see this type of thing in a small backyard pond, you might want to check ammonia levels in the water as well).

What You Can Do

When a pond owner finds themselves in this kind of pinch, the first instinct is to try and do something, anything that may help, and that’s usually when I get the phone call.  If the pond is small, heck, any air is better than nothing, so you could pick up a small aquarium aerator at Walmart if you have to.  It might help in the short term, although it will probably be underpowered for the pond long term.

Sometimes breaking the surface tension of the water will be helpful, and spraying water on the pond, ideally in a similar way that rain water might fall upon the water is at least something to try.  When you break the surface tension of the water, air from the atmosphere can enter the top few inches of the pond.  

I won’t go so far as to say this same approach would help much in a larger pond, but it’s worth a try if you can do it.  Remember the key is to break the surface tension of the water, not simply circulate more water, which is another thing I hear about from time to time.  A  pond owner might have a circulator going, or have an incoming stream or pipe that adds fresh water to the pond, and while these things are helpful in some ways, they may not affect the actual amount of DO in the water.

If possible, try to limit unwanted plant growth in the pond.  Plants aren’t all bad of course.  They add oxygen to the water while the sun is out and they benefit from photosynthesis, but when the sun goes down, the same plants start to pull oxygen from the water.  So a big messy algae bloom won’t be doing you any favors here.

Keeping a pond cleaner overall will help and we do this with the use of beneficial bacteria.  Limit any muck or sludge build up as best you can, or work to reduce what’s there and you won’t feed algae, or even duckweed so much.  You’ll also limit the problem of turnover or inversion which can also rob a pond of oxygen.  

Aeration Is The Key To Protection

I hate to sound redundant here, but I have to say, as I said to the caller with the dying fish, if you want to stop this carnage from happening in your pond, there’s one answer.  Pond aeration.  It’s really no more complicated than that.  Your fish need oxygen, and aeration delivers that throughout the pond.  It increases the saturation of DO in the water and helps maintain things, when the weather get’s tough.  Anything else, if it helped at all, would just be some kind of band-aid.

The key of course is to have aeration up and running before things get really bad.  Don’t wait until the fish start to suffer. Most aerators these days are pretty efficient and affordable to operate.  They need to be run 24/7, ideally most of the time, but in  particular as you go from spring into summer and the temps go up.  

 Finally I haven’t found anything to protect against turnover or inversion, any more than a good aeration system.  You still want to reduce build up of organic stuff on the bottom, but aeration will be the primary protection against this.

Taking some kind of proactive action rather than trying to respond to a problem once it happens is really the best medicine here and I can’t stress that strongly enough where your fish are concerned.

For a very well written and descriptive summary I’d suggest visiting Aqua Plant and read their review of dissolved oxygen in ponds.

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