Carbonate Hardness (KH)

This is the measure of calcium and magnesium salts which are present in the water, especially if the water is alkaline. Soft water tends to be associated with acidic conditions while hard water is indicative of alkaline water. If pH fluctuations are being experienced, it is worth testing the pond water for hardness. If you are experiencing low levels of carbonate hardness, you may need to add minerals to the pond as your koi need a certain amount of calcium and minerals for their good health. It will help to buffer the water which will help maintain a constant pH level (using Hydra pH Buffer). This can be done by putting crushed oyster shells in the filters , or by adding a proprietary product  designed for buffering the water in the pond. Certain medications also react differently  in soft and hard water, so it is important to know about your water conditions should a problem arise. Generally in soft water chemicals become more toxic, while in hard water they become less so.