Take note these were grown in freshwater. Have 7 plants left, $10 per plant. Take all for $45 collection in the east Sent from Singapore Reef Club mobile app
There could be various reasons. But one likely one is that it is bleaching due to excessive light. Gonio generally prefer low light conditions. From the picture, it seems to be placed at a location that's bright enough for SPS/Monti. Perhaps its too bright.
Would suggest to bring it to a more shaded spot.