The biggest factors in determining water quality are an unclouded pond environment, adequate biological filtration, minimal debris / sediment accumulation, and sufficient water circulation / aeration. 

If you notice that one or all of your fish appear to be sick, the first step is to correctly diagnose the problem.  There are a wide variety of potential life threatening fish illnesses, but they can be broken down into two primary categories:  bacterial infections and parasitic infections.  The medications used to treat the different illnesses are usually very different, so properly identifying between these two types of problems is paramount. 

There are several excellent books that outline the different kinds of fish / KOI diseases, so we will not go into it in detail here.  However, we can outline several of the most obvious and common symptoms and remedies.  For bacterial infections, the fish will usually exhibit some signs of stress like bloody streaks in the tail fins coupled with obvious lesions or bloody sores on the body.  These are usually found around the mouth, or on the sides or belly of the fish.  Another clue would be a cloudy haze over the eyes and a lack of energy and appetite.  Fungal infections are indicated by white fuzzy patches or growths on the fish.  Treatments vary, but typically the best treatment is to add pond salt to the pond, then add a medication like potassium permanganate, or pond fungus eliminator, and top it off by feeding an anti-biotic feed or immune boosting food like impact.   In some cases, an anti-biotic injection is required.  This is usually the best remedy, but not many pond owners are comfortable with doing this. 

Parasitic infections are not uncommon in fish ponds either.   Parasites can be introduced by new plants or fish in the pond, so always buy your fish and plants from a reputable dealer.  Warning signs of parasite problems include fish "flashing" or scraping their sides against the bottom of the pond, visible objects attached to the fish, small bloody spots, and sudden fish death by one or more otherwise healthy looking fish.  Again, the best first course of action is to add pond salt to the pond.  This will kill many of the free swimming parasites before they can find a host.  Other treatments include:  formalin,  malachyte green, or a malachyte / formalin combination.  There are many forms of parasites however, and the list of treatments is extensive so if you suspect you have a problem and cant diagnose it yourself, contact your local pond professional.  We carry a wide variety of pond fish medications, as well as reference material for diagnosing different ailments so we may be able to help.

Related topics
Spring cleaning
Winterizing your pond
Biological filters
UV Sterilizers

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