Northern Lights Auto DWC

I've topped this a couple times on the main stem. You can tell towards the center of the plant. Roots are massive already. All of the leaves look healthy; no nutrient burn. There are maybe 1 or 2 with speckles on it, likely from PH imbalance when it drank all of its nutrients earlier this past week. I have been adding about 550 ppm, but end up adding another 300-400ppm a few days later. I feel more comfortable doign this than dumping 800-900ppm, because I don't want to burn it. So, again, just monitoring PPM through the week. pH has been staying relatively stable. Water temps are maintaining between 62-71 F. I'd like it to be below 68, but the weather here is changing often and it is hard to keep my basement stabilized. I really like this strain from this seed company. This will be my third harvest, and this Northern Lights plant is BY FAR the fastest and heartiest plant I've grown. I definitely recommend growing this auto from Genehtik.