Many koi keepers know that common cooking salt has numerous beneficial effects on fish, not least a marked anti-parasite activity and the promotion of healing. Some people maintain a permanent low level of salt in their pond. Others add a low level over the winter to help the fish survive these colder months. Salt has many other benefits as it help tackle parasites and reduce ammonia and nitrite poisoning. Blagdon Pond Guardian Tonic Salt improves water quality with its built in pH buffer which guards against potentially damaging swings in pH, as well as helping fish to maintain a stable internal salt and fluid balance, which is essential to their health.