I am of the opposite view to the other members respecting the Betta. While there are always exceptions, a male Betta is not
a community fish. It should always be housed separately, or with substrate fish. I had a Betta years ago, he delighted in eating neons, and that experience is widespread. There are better fish to combine with tetra.
You need a group of any tetra species, six minimum but more is always better for the fish. But a 29g is not limitless in space so once you up the existing two species, I would consider one more as maximum, provided it is similarly a slow-swimming species like the two mentioned; something fast would not be a good match. Some surface fish (thinking hatchetfish) and substrate fish can be added.
I would also lower the temperature. Neon tetra last better at temperatures in the low to mid-70's, and 78F is about as high as it should be. All fish require more oxygen and more energy the higher the temperature, so it is always a good idea to maintain a temperature in the lower half rather than the upper half of their range, where feasible--meaning, depending upon what is in with them. They will be healthier at a lower temperature.
The pleco may be an issue temp wise too, depending what species. I would need the scientific name to say more on this.
We have fish profiles, second tab from the left in the blue bar, so you can find info on many fish including the Neon Tetra and Glowlight Tetra. Click on the shaded names to see the respective profile.