I would echo @Patrick_G's question. An uncycled tank could cause what's happening to your tetras.
Here's a handy link on the nitrogen cycle that might clear up some issues you are having. https://www.aquariumcoop.com/blogs/aquarium/nitrogen-cycle?_pos=3&_sid=19eb9cef6&_ss=r
When my 55 was full of rocks, I used to take smaller ones and arrange them to make a natural pot and then add gravel and plants in that. Add some anubias or java moss at base of those rocks and it looks natural. All my rocks were the same type so I'd end up with a terraced effect. You might be able to arrange something like that around the base of that wood?
I've used No Planaria with good success. Very hard on Nerites, no issues with my shrimp and other snails. Took over 6 months before I could put the Nerites back in without them going comatose.
Mine spawn all the time, but they are so fast most of the eggs or fry get eaten. I think I've had 4 or 5 make it to adulthood in the last few years. That's with no interference on my part and just letting them do their own thing.
Neon tetras.... Pretty little fish, but they can have so many issue,s and ugh... trying to catch them in a fully planted tank.. I still have nightmares about that.
Also, glofish (which I would have loved when I was a kid)
I have a couple feeder goldfish in my pond. They've been in there for 3 years now(?) and are tough as nails. They were kind of homely when I got them, but have changed their spots and colors a bit as they aged. Both of them were tri-colored when I got them and now have no black coloring and are mostly orange with some white.