yes, it could, but generally mushrooms are pretty hardy. rowaphose works, but takes time to work, and is pretty expensive, best used with a phosphate reactor/chamber.
if you're tank is not too large, i'd suggest doing some larger water changes, 30% from a reliable water source.
sometimes store that sell water, they mix with just salt water and tap water, with poor quality marine salt.
or you could get good RO/DI water and mix yourself with good quality salt like from Coralife, Kent Marine. Let it mix then sit for at least 24 hours before using. But i'm sure you know all this already, so I'll stop.
Check the temperature, during the summer, over 84 could make them shrink.
Any fish nipping at them, some fish nip at mushrooms.
Any corals stinging them, there are like thousands of possibilities that could be wrong, they're normally pretty hardy.
Good luck, some photos, and detailed water parameters and upkeep info. would help. Temp., ph, salinity, Calcium, alkalinity, also could test for copper too...
