| I do not like the idea of a 50% water change once per month. Too much fluctuation of conditions is likely. In rare circumstances, it may be fine, but I think such circumstances would be truly rare given how we stock koi ponds. IMO, the weekly (or more frequent) water change should be as much as is needed to have nitrate under the desired limit of nitrate for the entire period between water changes. (Nitrate is relatively easy to measure and thus convenient to test. The other pollutants removed by water changes are not readily tested, but are of concern.) Or, to have alkalinity remain above the desired minimum level at all times. In soft water areas, the alkalinity test will be key. In areas with hard water, the nitrate level will be the more important on which to focus. However, the amount of water change should be no more than what can be done without the pH and hardness differential between the pond water before the water change and the pond water after the water change being materially different. Folks will differ on what they consider 'material'. I cosider a pH shift of .5 to be too great; and a hardness shift of 20 ppm to be too great. If the shift is material, then the water changes should be more frequent so that the pond water more nearly matches the source water (whether the 'source' is direct from the tap, or water that has been pre-treated in some fashion [such as use of a softener, RO unit, purifier, etc.]. I generally recommend trying a weekly water change of around 20% to those hobbyists who do not monitor their water conditions and are not familiar with the behavior of their water through experience. Larger water changes may well be possible, but one should understand their water or test carefully before changing larger volumes. I typically change 30-35%, and with my prior smaller pond I typically did 50% per week.
Every pond differs, so simple recommendations are not necessarily appropriate. |