I'm guessing you have a 20 gallon tank.
You have good filtration, and larger regular water changes helps along with plants to keep the water clean with large fish loads.
If you didn't have to worry about the platys breeding, i would say add the neons, however in a couple months there are going to be many more platys in that tank.
With that size tank, I would add more fish, since i love plants, but i love my fish too and keep my tanks well stocked.
You have good filtration, and larger regular water changes helps along with plants to keep the water clean with large fish loads.
If you didn't have to worry about the platys breeding, i would say add the neons, however in a couple months there are going to be many more platys in that tank.
With that size tank, I would add more fish, since i love plants, but i love my fish too and keep my tanks well stocked.