So I changed my water a few days ago and everything measured well... This morning I woke up to 2 dead cories, I did a 20% water change and let it go but then this afternoon another one died and so I retested water and it was still normal. Temp: 76, pH: 7.2, GH: 8, KH: 2, NH3/4: 0-0.25, NO2: 0, NO3: ~10. Now it's been a few hours and another one is dead...any ideas what is happening!? This is awful! I don't know how to fix it because nothing is standing out as the problem!