Get it out of the sphagnum. bellatulum needs an airy mixture that is
calcareus, and definitely not acidic. Between the moisture and the
acidity, it is bad for bellatulum. To revive a weak plant, try
coco-peat, very well rinsed to remove salts, with lots of perlite and
some oyster shell. It will remain moist, while prividing lots of air.
Take care, Eric Muehlbauer