Appreciate your time. I’m going away for 2 weeks so will try a local fish next that hasn’t shipped recently. The second fish that died was mid day and wasn’t due to an attack that I could see. I saw it swimming, started a work meeting, and 15 minutes later it was dead. Hoping there isn’t a bobbit or an unfriendly crab, but those don’t hunt mid day, right?That should be fine, no none of that should affect ph or water quality significantly tbh.
Honestly i cant see anything but bad initial fish health, equipment malfunction, or external actor (person/child, animal, or tank animal) being the cause. Everything else checks out.
Anyways, only way to find out is to put another fish in, preferably locally sourced and has been in their tanks for while (maybe 2 weeks+) so you can get it into your tank in the shortest amount of travel and know its not going to die from things that have happened to it during international shipping.
Also check in to your tank at night, you might see the culprit.