I agree with D-Nak. Wipe down the tank and rinse well between 100% changes. I know you say it's not attaching, but keep it with high flow. They will live a very, VERY, long time with flow that is too high, and, THAT, will keep them from disintegrating - they may not look too hot, but will keep them from melting overnight. Too low flow, they rot quick and continue to go down. If you can catch it fully inflated, do what ever it takes to keep it that way, alter lights, alter flow, mess with water, etc. They're not all the same. Some like high flow, some like low. High flow is healthier for them, but some will look good with low flow. Not all the same. They can be a very slow turn around.
Try changing your lights too. Raise them up (distance), and intensify them. I know, sounds silly. Try it. Time going by with no changes is a problem. Keep doing 100% changes every day. Sometimes all efforts won't work, too much time goes by or the specimen is in poor shape to start. Best of luck.