I agree with the yellowing, except in this case, the whole plant was gone within a week and would not recover when I moved a portion of it back into one of my neutral tanks. It was really weird since I've had hornwort do just fine in that tank before. I had taken the original bunch out because it was looking pretty messy...but then after a few months, i regretted it and got another bunch (from a big-box pet store). Maybe i got a bad bunch. I've certainly gotten bad batches of anacharis from there, too, but my mbuna looooove to eat anacharis.