Koi and goldfish excrete ammonia from their gills. Urine and solid fish waste break down into ammonia. Decaying plants and algae also release ammonia into the pond. Uneaten fish food will also decompose and release ammonia into the pond. Ammonia is toxic to fish. Chronic eXPosure to low levels of ammonia will damage the gill tissue. This prevents normal gas exchange across the gills. Fish will become weak and susceptible to a variety of diseases. High levels of ammonia will result in rapid fish loss. It is impossible to see or smell ammonia in pond water. The only way to know if ammonia is present in the pond is with an ammonia test kit. Use the PondCare Liquid Ammonia Test Kit to accurately measure the ammonia level in ponds and water gardens.