Sand being bad for plants? As apposed to growing plants in fake colored gravel? Sand is fine. Kitty litter in the bottom works great BUT you have to get the right brand. If you dont want to risk that you can always just but root tabs. Those last a long time. Or if you dont want to do THAT (lol) you can but a bottle of fertilizer and mix that in with your sand. Not that hard. Seems like work buts its really not
If your betta is eating sand, its retarded. Sorry to say but its true. And they most likely used a too fine of sand that gets stirred up easy. They prob didnt eat it but breathed in too much dust.
Anubias (tie to driftwood)
Crypt (so easy you dont have to do anything)
Sword (heavy root feeder but if you fert the sand your fine)
Anacharis (super tall background plant)
Java Fern (dont have to do anything to this plant)
You can get some good looking tanks with little effort. One thing to make sure is make sure you have enough light. For a 8 gallon tank you want 20 watts of light.
This is my old tank with good light, root tabs, and easy easy co2.