When it is time to change the water in any environment that you have fish in it is not a great idea to change all of it. Fish do not like to have any changes that are sudden in their environment. Change on temperature, pH, or even chemistry of the water. If you have a good filtration system it should have a biological filter and also a mechanical filter. This is just like ponds found in the wild. The filter that removes the fish waste that is dissolved is the biological filter. The filter will turn the waste into nitrite and then into nitrate. This is all done within the filter system. Nitrate is harmless to the fish but it will allow build up in your pond that can harm your fish.

There are some water plants that you can purchase which will help remove the nitrates. But it would take so many plants to remove the amount of nitrate that you need them to. Some people use a trickle tower to remove any nitrates in their koi pond but they are not that cheap and by giving your water a partial change is much more cost efficient. Which is like ponds found in nature. Water changes should be done often however they only need to be changed about ten percent every two weeks. When it is time to change the water you need to also check for the nitrate level by doing this it will help prevent and discoloration in the koi pond. You can test for nitrate using a test kit that will let you measure the nitrate level, pH, nitrite, and oxygen level in your koi pond. Similar to ponds naturally occurring in the wild.

If you are planning to use tap water when you fill up your koi pond you should also use additives that you can buy at the store to remove chlorine that has been added to the water. Also if you have a few hours and a place to store it the chlorine will come out of the water while it sits.