he most likely didnt like the spot you placed him in.. try to give him a spot with moderate flow, just enough so his crown gently sways in the water so he can sift out food from the water column. If it is too rapid or there is not enough flow he will starve. If he ditched his tube he should make a new one assuming hes alive, it may take awhile. Ive had mine for 5 months or so and ive never had a problem with him.