Neon Tetras Dying Off

[Joonkun]

some more sensitive tetras have real issues with higher ph. sure stable ph is usualy more important as the fish will adjust. but something like neons are really senstive and keeping them under the wrong ph can really affect their ability to stay and keep healthy, fight of diseases as well as stress them out.

[Cyberghost]

I currently have 3 neon tetras remaining in my tank. I am losing a fish every night and trying to figure out what is killing them. Yesterday I had one floating in the tank and it looked like it was attacked. Not sure if something was picking at it after it died, but something is gunning for them. One of the female swordtails has been getting aggressive since the additional fish have been added. Plus I think she is pregnant again. Could she be going after them when I shut the lights off at night? When the lights are on there is no aggression being shown to the tetras. Could it be the snails or the pleco?

Has anyone run into an issue like this with community fish? If so what did you do to fix the issues?

I had the exact same problem at the beginning of my current setup, lost a neon every night until they were all gone, once found one that was still alive, but injured. I blamed it on my plecostomous because I read they liked to eat the slime coats of some fish. The fact that the injury looked like the general shape of the plecos mouth enforced this theory.