HELP LTA WONT TAKE HOLD

[Wetback]

We purchased a beautiful purple lta on Saturday,did all the usual stuff and placed in our tank...Very pretty but he won't plant himself He blows up like a balloon and floats all over.I am sure this is fun BUT we are afraid he will puncture or something..We tried to corral him in a cozy and placed a rock to try and wedge gently but tonight he JUMPED Please someone share some advice on what to do..tks in advance Norberto/Tina