I have lost five koi and several small golfdish in the past three days. I am so sad!!! I am trying to figure out what it is and am thinking it might be a toxic plant???? We also just started filtering the water thru a hydroponics tub as well. We have a Hawaiian Ti plant and two crotons in there. I searched on line to find out that crotons are toxic so I removed those. I read online that elephant ears are toxic too, but the lady I got the elephant ears from had them growing like crazy in her pond. Help!