An established pond with healthy fish should be checked every month. It is only when you notice something out of the ordinary, and possibly during seasonal changes, that an additional test or two might be prudent. An ounce of prevention is worth a pound of cure. A simple test, at the right time, can prevent a minor problem from becoming a catastrophe. When starting up a new pond or Bio-converter system, daily tests may be required until the converter comes on line, then weekly for a couple of months until the system has stabilized.

The desirable base lines are:
PH level = 7.5 - 8.5
Hardness = 50 - 180 ppm
Alkalinity = 120 - 180 ppm
Ammonia = zero is the best, because besides poisoning it blocks the oxygen transfer from the fish's gills which is a painful issue.
Nitrite = 0 - 4ppm
Nitrate = 0 - 200 ppm
Temperature = 26o - 27o C
Dissolved oxygen at a temperature of 50oF - 9mg/lt.

The moment you have decided to introduce a Koi into your garden pond or the drawing room tank, you have taken every responsibility to nurture it with utmost care. The concept of care, over here, goes far beyond the arena of simply feeding and putting enough waterweeds in the pond to provide oxygen. A responsible Koi keeper must be smart enough to understand the pond water chemistry and the relevant science.
Before bringing the cute kids to home, ensure that you are totally equipped will full range testing kits and measuring meters. Prevention is always better than cure. Kits for measuring the scale of pH, ammonia, nitrite and temperature are of prime significance, while kits for measuring the scale of alkalinity, salinity, nitrate and dissolved oxygen are moderately essential, while again the kits for measuring the scale of chlorine and hardness are of low significance - yet nice if you have. And lastly but chiefly the pond must be well equipped with high quality filtration mechanism. These are doubtlessly the vital things, but above all the most important tool is the owner's technical knowledge regarding the proper use of these kits and regarding the desirable level of the parameters.

Once such a baseline is prepared, the rest are laid on the shoulder of water testing kits and measuring meters. The kit contains a full set of water testing peripherals such as test tubes, holding trays, computer-analyzed color cards, instruction manuals. Parameters like certain salts, dissolved oxygen, PH, alkalinity and salinity are measured by the meters meant or specific purpose.