They will eat veg try weighting it down with something like a rock? And the might gather around it.
Do you know what species it is? Which way are the stripes? Do they run up the body or down it? If its up the body do the lines all kind of merge near the tail or do they stay divided between the black and yellow?
Out of all the striped headstander species one might work in your tank - you would have been better with the spotted ones though.
Wills