I would sooner trust the water department than Dr. Roddy Conrad. The water department certainly has nothing to gain by their statements. (I am not implying that Dr. Conrad does either, so don't go there). If you have any amount of ammonia in your water after a water change, it is a stressor to your Koi. How fast your filter absorbs the ammonia, depends on your system and your fish load. Why would you want to burden your filter with additional ammonmia when you can remove it entirely with chloramex? Remember, not everyone uses Amquel, or anything for that matter, to bind the ammonia. Amquel also tends to stay in your pond, chemically, and when it builds up you can smell it. This is also a bad thing for Koi. If you only use sodium thiosulfate, then it is a mistake, and if you use sodium thiosulfate and a binder it can be dangerous. Your Koi are valuable and I don't understand using a product, that has potential dangers, over a product that is safe, to save money. I buy Chloramex in a 55 pound box and that lasts me all year. Keeton Industries has it for only $250.00. It seems like a small enough price to pay for water than is treated INSTANTLY.