1st grow purple lemonade

Well into week #2. All 5 purple lemonade are on day 9 and looking ok i think. 3 of the 5 have taken off and 2 have seem a little bit slower in growth rate. I also noticed 3 of the 5 have skinny purple stems compared 2 the 2 larger ones that have thicker green stocks. Im not sure what this is due to from this being my first indoor grow. Also plants seem a little short to me. Not even sure if the plants are growing at a proper rate. I also had a problem with about 15 gnats spotted over the course of the last week. As a result i have stopped watering for the past 3 days to dry the soil out to prevent them from breeding further. I did water a tiny bit today at the base of stem on all 5 plants but not much at all. I have been able to maintain a pretty steady temp of 25c and a RH of around 60-70%. Any suggestions on the gnats or skinny stems would be great! Happy growing