Toxic Pollutants & Their Effect on Fish Health

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Once water temperatures increase in the summer months, fish become more active and produce increasing amounts of waste, leading to potential water pollution. Fish produce waste in the form of ammonia, which is broken down into nitrites then nitrates by beneficial bacteria. Both ammonia and nitrite are very harmful to fish, even in very small quantities. Ammonia, in particular, is more toxic at high temperatures and can cause severe problems. In fact, water can hold five times as much dangerous ammonia at 77?F as opposed to 41?F. The effect on water quality is exaggerated by a high pH, resulting in the formation of more toxic ammonia.

High nitrite levels are also more dangerous in low oxygen water levels. Nitrite causes the hemoglobin in the fish's blood to form metheamoglobin, which cannot carry as much oxygen around the body of the fish, therefore making fish lethargic.

Nitrates are relatively harmless to freshwater fish and act as great fertilizers for plants. However, they also encourage the growth of unwelcome algae, such as green water or blanket weed. So, be sure to test the water quality every few weeks with a kit.

If there is a noticeable reduction in water flow, you can back flush your pressure filters and gently rinse any biological media in a bucket of pond water. (Depending on your type of filter, its biological media can be anything from plastic cylinders/spheres to spaghetti-like strands to foam pads.) Biological media should never be washed under the hose; chlorine contained in the water kills the beneficial bacteria. Remember to never scrub the media clean; simply rinse off any excess sludge or debris so beneficial bacteria will remain intact and active, restarting the biological process.

Brett Fogle is the owner of MacArthur Water Gardens and several
other pond-related websites including
and He also publishes a free monthly
newsletter called PondStuff! with a reader circulation of over
9,000. To sign up for the free newsletter and receive our FREE
'New Pond Owners Guide' visit MacArthur Water Gardens today!

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