Dark green and smells terrible

Question:

I have a ninety gallon pond with small water fall. I have only had the pon since May of 2007, so I am quite green on how to take care of it. Until this weekend I have had minimal problems maintaing the clearity of the water. When feeding the fish yesterday I noticed that my water was quite dark (green) and smelled terribly (like it was stagnet). The fish are coming up quite a bit to the water fall and letting the water run down on them. What should I do? I also need to know what needs to be done with the pond to prepare for winter. Thank you, Tracy Anderson

Answer:

It sounds like the pond has developed a nitrite problem. Ammonia and nitrite are very toxic to pond fish and will eventually lead to their death. The pond water should be tested immediately for these toxins and all feeding discontinued until the levels of the toxins return to zero. Some partial water changes may be needed to facilitate the pond water becoming healthy again. Don’t forget to remove chlorine if city tap water is used. It is also best to add a water conditioner that neutralizes the ammonia and or nitrite in the pond water and helps your fish to restore their slime coat and breath easier.