MSG- all of the plants are in riparium planters (see the Riparium Supply in the vendors section of the forum). These have suction cups on the back, so they are hanging at the water surface, thus keeping the violets above water.
I have not tried neem oil or peppermint oil. I was not sure what sort of things were non-toxic to aquatic life. In the tank I have a few fish and some shrimp and snails. (little bit of everything, kind of).