The curtine plus could have done it? I am no expert but if you treated the entire pond and there was that much chara in there and you killed it all in one swoop. You had a D.O. issue I bet. Even with your windmill air. That's a lot of chara killed. Plus they say the weed uses D.O. while it's dieing if I remember right? Lets see what someone else has to say that has a little more insight but I bet you had a mini D.O. crash!

The only difference between a rut and a Grave is the depth. So get up get out of that rut and get moving!! Time to work!!