Hey fellow fishkeepers! I need to discuss a recent issue regarding my fish and fish tank. On June 28th, I added 2 pseudomugil paskai and 1 galaxy rasbora to my tank. On June 30th, I returned the rasbora to the LFS and brought home 2 more pseudomugil paskai. ----- On July 7th, I came home from work around 1 - 2 AM and found one of the dead. I do not recall the water parameters but the fish itself did not show any obvious wounds or signs of disease. The day prior it looked and acted normal. ----- On July 8th, I came home from work the same time and found a second one dead. Again, all was fine during the day with its behavior. These were the water parameters: Ammonia 0.25 PPM Nitrite 1.0 PPM Nitrate 15 PPM I noticed the fish's tail fin looked damaged. I performed a 50% water change. ----- I arrived home this morning and found a 3rd one dead. I will post pictures of its condition. It does not look good... I also took note that several pieces of dwarf hairgrass were floating at the top, as if something disrupted the roots. Water parameters: Ammonia 0 PPM Nitrite 0.5 PPM Nitrate 5 PPM ----- I have a feeling that this has happened because my tank was overstocked, and perhaps I caused aggression by not having at least 6 neons. I have never seen any of the fish harass each other, but I'm not home from 3 PM to 1 AM. I do not suspect it to be a water quality issue. I do a 20%~ water change every other day and a 50% water change on the weekends. My tank is a 12 gallon. The inhabitants are 3 guppies, 1 female honey gourami, previously 4 neons (down to 1), and some ghost shrimp. My perception is that the guppies are friendly and curious, but never nip at anyone. The gourami is sweet and has never shown any signs of aggression. My plan was to save money for a larger tank and properly house everyone, but at this point the remaining neon would be better off returned to the LFS. Does anyone have a good idea of what exactly happened? Thank you for your help!