Help, fish dying

I'm at a loss and I'm not sure what to do. I currently have a 36 gallon planted tank with mollies, platys, neon tetras, algae eaters, and some baby mollies. I have a few nerite snails, a mystery snail, and quite a few neocaridina shrimp. I started my tank around May 2025 and everything was fine. Over the past few months I have had quite a few deaths, my original guppies have died, my platys are dying, a mystery snail died, and neon tetras have died. I took a water sample to a chain pet store and to a family owned pet store and they gave suggestions on raising my PH, raising my alkalinity, and getting some more plants. I already have dried coral in my tank and calcium cuttlebones. I also have a bubbler that is about a foot long to aerate the water. Testing my water my nitrates are between 0-20, my nitrites are between 0-.5, chlorine is 0, ammonia 0, alkalinity is between 40-80, PH is around 6.8. I typically keep my water somewhere around 77-80F. The most recent platy that died had a hunchback and looked sickly. Today a neon tetra was partially eaten before I saw it to take it out. I don't want to keep losing fish and I would eventually like to replace what I have lost, but I don't want to add anything new until I figure out what is going on. (Marked NSFW just in case- fish deaths)