If you have read my guide Fish need oxygen too, you will know that oxygen in pond water is vital for fish to survive.
The ideal level of oxygen in pond water is 11mg DOC (Disolved oxygen content) per litre of water.
"So how do you measure that" I hear you cry, "do you want me to count the bubbles."
Err No, you will need to purchase a test kit.
This is basically a few chemicals that change colour when added to water.
The more DOC present the greater the colour change.
You should also be testing your water for Amonia, Nitrate, Nitrite, pH and Salinity.
Changes in the make-up of your pond water can have a dramatic effect on your fish, especially Koi
If you have Koi that are looking a bit pink, this is probably due to stress caused by chemicals in the water, lack of oxygen, high amonia or nitrite etc.
In short, get a test kit and get your water sorted.
We have lots in stock, all come with easy to follow instructions and all the pots and droppers etc that you will need.
Bob De Feitas