u/Turbulent-Event-8988

I don't even know what I'm looking for here... encouragement? Validation that I'm not the worst fish mom in the world? Or confirmation I should just give up the hobby altogether. I'm feeling so incredibly upset and discouraged. These last two weeks have been the roughest in my 8 years of keeping aquariums.

For reference, I have 13gal shallows for the males and I just set up my first attempted sorority two weeks ago in a 28gal shallow.

Two weeks ago (the day after setting up my 28) I woke up to find 2 sudden deaths in the MALE tanks. No symptoms, no issues. Water parameters were completely normal. The otos and shrimps were all fine. Just 2 dead bettas. I checked the temp, temp was reading normal and I double checked on a float thermometer, totally normal. Weird, but they were pet store rescues, so maybe just their time? Three days later, one more sudden death and three more severely ill. Again, only the bettas, all water parameters normal and temp normal. All otos/snails/shrimp totally fine. The three that were sick but still alive looked AWFUL, totally clamped fins, super dark, stress stripes. I took samples from each tank to an aquarium store just in case my kit was expired or reading wrong. They said everything was perfectly balanced and fine. I thought, maybe it's the newer food I'm feeding? So I switched. They got worse. I tried floating them in heavy tannin water drawn from the 28 that had fresh mopani, one more died. So a total of four bettas dead within a week. The other two, at this point, do seem to have recovered. I finally FINALLY figured out the culprit WAS the heaters. They would heat well enough during the day but during the temp drops at night they weren't heating the tanks. But during the day, when I took my independent readings, everything looked normal, so I just didn't consider the heaters.

Moving on to last night, the 28 sorority was SO DARK (fresh mopani) that I couldn't see the bottom and I didn't want the plants to die, so I was doing a water change. I was just holding the siphon at the top because there wasn't any mulm to clean up, and I had my hand right on the hose, right near the tip. The girls were curious, but keeping their distance as usually they do?! I have never ONCE IN MY LIFE had a fish that actually went anywhere near the siphon. But one of the girls that was on the other side of the tank just charged it. Zipped over and before I could even react she was decapitated and stuck inside the siphon. It was an instant death with no pain, but oh my god it was the most awful thing. And I just. I don't know what to do. I don't know whether the sorority is new enough to replace her (which sounds AWFUL, just replacing her) but I don't want the sorority to fail because there's suddenly one less fish. I just want to give up altogether. They were totally fine and getting along well, established hierarchy and territories, and now everything is in chaos. I spent a good two hours last night crying. I just. I don't know how to come back from so much fucking useless death in such a short time.

TL;DR I had 4 bettas suddenly die due to heater failure and 1 betta decapitate herself during a water change in less than 2 weeks. I don't know if I can do this anymore.