Dwarf Meyer Lemon Tree Has Scale & Shiny Leaves - How Should I Treat?

My Meyer lemon tree has a small cluster of soft brown scales on the trunk, and some sticky/shine on the leaves. I have also noticed a gnat or two flying around the plant over the last several days. Tonight I removed the scales, but what should I do to rid the plant of them completely? And how should I clean the sticky leaves? I purchased the tree this past winter (it is a 1-2 year old tree), and have been keeping it indoors under a grow light because our weather has not been nice enough to move the plant outdoors yet. Where do the scales even come from?