Hi everyone, thanks for taking the time to read! I have a well established lightly planted 29 gallon. After the gazillion guppies finally died off and rehoming a rather large common pleco, we restocked with: 1 albino cory 2 yoyo loaches 2 platys 6 serpae tetras 6 neon tetras 1 male fancy guppy who I think will live forever Things have been going well for about 3 months. (Weekly water changes, nitrates stay around 5, 0 ammonia, 0 nitrite.) Last night, I saw a neon had died. This morning, two more were dead. Two are fine, one was kind of floating nose up and missing its tail. The guppy was hanging out in the top corner near it. Immediately checked water, was at 0,0,5. Temperature was at 83, up from normally 79. So I unplugged the heater and headed to the store to get a new one, figuring that one has malfunctioned and just in case. When we got back, the neon with no tail was swimming near the other two, as normally as he can. The guppy was also near the injured guy. Just noticed it looks like one of the other beyond has a bite out of his tail also. I have a 55 gallon cycling but it's definitely not ready yet. I'm looking to move the loaches to it and increasing their numbers. Then we'll get some more corys for the poor lonely guy in the 29. So, who is the most likely culprit, the guppy or the loaches? Should I isolate the guppy? Everything says yoyos shouldn't be with neons but I've never seem any aggression from them, maybe they're jerks at night? As I'm typing this, I'm watching the tailless neon just hanging in the lower corner with the guppy hovering just over top of it. So, any thoughts, ideas, or experience?