My moss ball looked like that, some algae growing on top and a bit mushy. I followed a suggestion in an online source and rinsed it off in cold tap water, then put it in a cup of water in the refrigerator for 24H. It really perked it up, so now I do that every few weeks. I've used plain seltzer water a couple of times and it seemed to like that as well. Evidently the lakes they grow in naturally are in colder climates (northern Japan, Iceland, etc), and also they are constantly gently rolling around so not picking up stuff as they might in our tanks. So you might consider that. Good luck with it!