Katie, you'll have to check the plant threads.
From what I have been trying to learn the higher the wpg, the more you need Co2.
James, you could always just get a glass top and 2 10g lights.
2x19=38/10=3.8wpg
But check your bulb, it may only be 15w instead of 19w.
That's how mine was before I redid it.
Moneywort, Anachris, Java Fern & Moss, Marimo Ball, Hornwort
Those should all be low light.