The more advanced solution to chlorine and other toxins is a water purifier. But, as when buying any Koi equipment, you do need to ask some pertinent questions about whether you need one, and how effective they really are.

First, you need to know what's in your water supply, and which chemicals are potentially a problem. The simplest way to find out what's added to your water is to ask your water supplier. But be aware that water companies adjust additives to suit the current situation, so toxin levels may fluctuate. For example, although water companies may not routinely add pyrethrum, they will add this insecticide to deal with occasional wildlife in the water. If pyrethrum is in your drinking water on the day you use it, then your Koi are in serious trouble. Similarly, a lab report on a particular sample of water can only tell you what's in the sample, not what's in the water at other times. So you need to provide for all eventualities.