She grows slowly

75-85F? 25-30C? Relative Humidity plays a role too as far as what is "optimal". If you control both with a AC/heater/dhum/hum then you can google "VPD Chart" and follow that for optimal growth -- has to do with controlling water potential relative to growth phase. these factors will control rate of root uptake. For 3 weeks that looks like good growth. Genetics will play a role, so there is variance. Plenty of nodes there, it seems. If you want longer internode length, raise light ~4" for a few days and observe stretch until you like it and then adjust as needed. Your plant looks fairly healthy, but does have something going on. P, K or S... consider recent behaviour, reference labels and understand what you have been feeding. If it was a hot soil to start, it could just be fertilizing a bit too early and getting tox/lockout slowly building. So, deduce what is causing that problem quickly before it progresses. after checking nutes section of diary: If you have been feeding what has been listed, dial it back.. Let soil nutes get absorbed and wait for hint of deficiency to start fertilizing. If you buy or mix your soil consistently, you can preemptively do this in future. For example, start at 1/4 str the previous week and slowly increase to normal over time. Once you get to full strength, it's even more important to get ~10% runoff. Avoids buildup / concentration due to evaporation+time. Some soils, like FFOF, can last 3-4 months before they need a drip of fertilized water. That's a "hot soil".