Auto Massassin First Hydro Grow

Through week 4 I decided to do some Low Stress Training to take the focus off the main cola and spread the energy around more evenly. A couple days after bending her over and she's right back on track with all of the lower nodes forming branches and becoming a lot more bushy. The Root development has been outstanding and has grown by nearly 10 times its mass in just a week. This will be the 4th week I didn't changed the nutrients and I believe there is plenty for the plant to still thrive on, if I notice a deficiency then I will be amending it. I plan to change the reservoir around week 5 as there is still roughly 10 litres remaining. The PH of the water has been altered as it dropped down to 5.5 and i'm not sure why? After amending this I monitored it over the rest of the week and it hasn't moved from 5.9PH I'm keeping the LED 18 inches from the plant and am still looking to get a PAR/LUX meter so I can properly adjust the height to what they need. As the weather continues to get colder so does my tent but it seem happy sitting at 23'C during the day and 18'C at nighttime. Just waiting for this girl to pop her pistils and show me the flowering signs.