Flow bags containing an aluminosilicate sorbent with the specific high ability to bind ammonium cations NH₄⁺. Ammonium compounds are the first products in nitrogen transformation of proteins. When the pH of water increases above 7 the ammonium cations can turn into free ammonia NH₃ which is toxic to fish. Using of Filtrax/Aquafix NH3 permits to avoid this danger and also reduces the possibility of forming further products of nitrogen transformation – toxic nitrites and nitrates which promote algae growth.