My pond of over 20 years and 1800 gallons is having issues. Lost 2 fish yesterday and 4 today... Recently had a problem about 2 months ago where the fish waste in the pond s 3 bArrel filter got flushed in the pond by accident. At the same time as a sudden ammonia spike ...so a full water change and filter cleaning was done. Most of the fish lived and were fine till now. These kind of things never happend before with my pond only more recently have things been going wrong, before it held roughly 20 koi no problems at all for over 9 years, now this...I'm at lose and need all the help I can get.