Ready to give up on fish

[FishyFishy!]

There is definitely something going on. You need to get to the bottom of it asap. Have you checked your tank at night for massive Eunicid worms that might be picking the fish off? Get a grounding probe for stray voltage. Start a quarrantine procedure for every fish going into the tank. Try feeding them something different. Etc.

There are a tonne of things to do before giving up. I understand giving up after all options have been exhausted. But until then, put your thinking cap on and figure it out.

I would do a quarrantine system for sure. Start it up, see if there is any random deaths. If not, your display has an issue.