Oh I believed you when you said your plants hadn't caught any. That is a moranensis type plant, possibly a hybrid and will catch gnats. It could use a lot more light. The leaves are quite etiolated and this is probably why the gnats are not sticking. For reference, I grow mine about 12-14"" under 6 bulb HO T5 fixture. They don't need this much light, but it gives them nice colors.