Were any new corals, especially leathers and/or Sinularia spp., added around the time you began noticing change? Any corals in the vicinity acting strangely? In general, these corals do not acclimate well to lighting and reduce in bubble mass when too much light is upon them. You mentioned that the change began before the new lighting (were original bulbs replaced with new ones?) addition so even though I would not count out photo-acclimation, it would be odd to place it as the sole culprit. Do you have a dawn/dusk lighting scheme? If so, does the deflation of bubbles begin before the dusk effect (all lights on), during the dusk effect (only actinics on), or after all the lights go out? Expansion of tissue/bubbles during the daylight and retracting at night is quite normal, but considering this came out of the blue and hasn't changed in months I ask, any changes in husbandry such as added chemicals/additives since, etc? Sorry if the questions seem redundant, but my first inclination was budding by the lower lobe...