If your fish hang out at the bottom of the pond, or act restless and lazy, then it's likely that your pond is suffering from poor aeration.

When oxygen levels drop below 7 PPM it not only affects the ability of your fish to breathe, but it also negates your pond's bio filtration systems. That's because optimum bio filtration results require large quantities of air. When bio filtration degrades it results in the buildup of toxic ammonia levels. This, in return, causes stress in your fish which can result in lethargy and even death.

Your immediate first aid calls for increasing oxygen levels at once. Unlike chemical treatments, you can't cause any problems by putting "too much" oxygen into your pond. The easiest way to maintain oxygen levels is to run an aeration pump 24 hours a day. If you are already doing that, and your oxygen levels are still too low, then either your pump is defective, undersized for the pond, or your water temperatures are so high that the water is not capable of retaining sufficient oxygen. Treat whichever of these conditions exist.

Once you have cured the oxygen generation system problems, its time to test your water for ammonia, nitrite, and pH. It's also a good idea to test for total alkalinity and hardness. Adjust any levels that are out of normal ranges using pond additives that are designed for each problem.

If you found multiple problems, or suspect that you have a general water quality issue, then you should commence a daily changing of 20-40% of your pond's total volume until you have turned the water over twice. Of course, you need to use chlorine-free water. After you have turned the water over twice you should perform all of the tests that I wrote about earlier and make any required adjustments.

If your fish do not recover, or you are experiencing kills, then you may have a parasite or other health problem. Check our article archives for potential solutions.