King British Safe Water biologically neutralises organic waste produced by fish. Poor water quality in ponds is a major cause of stress in fish & can be fatal. Fish release ammonia through the gills & by going to the toilet in the water in which they live. Uneaten food & plant debris also decomposes, releasing ammonia, which is toxic to fish. Ammonia may be converted to nitrite, which is also toxic and may kill fish if left untreated. Safe Water oxidises ammonia & nitrite into nitrate - a relatively harmless substance that can be absorbed by plants as foods & is easily removed by regular partial water changes.