!!!root fungi!!!

Keep them and carry on -

 

I agree

 

Lol, dude, don't freak out keep the plant, cut the bottom end if it looks fuzzy and fungus-ridden, and chuck it back in, it'll keep growing out the top, and if you stick it in the gravel, it will root...
well, it could even send out roots while floating.

Your fish haven't evolved to breed while elodea is in the water, they spawn when there is a cover giving plant in your water, right, so when you take it out there probably isn't a place to hide and give cover to the fish. nowhere to feel safe or hidden, fry also needs to hide from bigger fish etc, and some fish prefer spawning when theres cover to lay eggs on, or to tend to the fry and protect them etc