This information was first posted in our "Question of the week."
The number given by an ORP (ORP stands for Oxidation Reduction Potential) meter is a direct index to the pollution levels of the pond. Unlike most of our other water quality readings, lower numbers are bad, while higher numbers are good. Readings below 150 indicate a pond in need of significant improvements. 250-400 is the range of healthy ponds, and conditions which promote good fish growth. High numbers between 475 and 550 reflect active Potassium Permanganate use, which should kill Koi parasites without harming the Koi. Readings over 550 should not be allowed to persist for more than 15 minutes because of likely damage to the Koi’s gills.
ORP meters are very useful for a quick indication of the relative health of any pond. ORP reading can help you determine if your filtration is working properly or if you need more filtration. To learn more about what increases and decreases ORP readings, how to use an ORP meter with Potassium Permanganate, as well as what to look for when buying a meter, you might want to consider purchasing the $3 ebook on “ORP Meters” from the K.O.I. store: