Hi all, I’ve had two 10g cubes with the same chemistry running for 2 years now. Each contains an ocellaris clown and generic cuc, and one contains a rainford goby. Every other day I alternate between PE mysis and a mixture of Hikari Seaweed Extreme and TDO Chroma Boost pellets. Fish have always been healthy with no signs of parasites. Yesterday was a Mysis day and the clown housed with the rainford goby refused to come up and eat anything. This was unusual but I shrugged it off as she otherwise behaved normally the rest of the day. This morning I was immediately concerned because she was not in her usual hiding spot, nor anywhere obvious. I eventually found her on her side in the sand bed near a corner of the glass. She was breathing rapidly, paled out, and with “dead” eyes. I immediately removed her from the dt into a qt bucket and observed until she passed in the following minutes. All other fish (including her goby tank mate) are perfectly fine, and testing this morning confirmed no parameter swings since last testing 3 days ago. I noticed a large discoloration of her insides through her pale scales, and coupled with her abnormal aversion towards feedings the day prior, assumed impaction/ intestinal rupture of some kind (see attached image). I’m still a novice to the hobby, and wondering if anyone could confirm my suspicions or give an explanation to these events so that I can avoid such mortalities in the future. I know fish mortalities can be unavoidable, but hoping to gain understanding as this one may be a reflection of my husbandry. Any responses would be appreciated.