Growing in promix hp with 20 percent perlite. Plant has been growing like crazy but yesterday some leaves started yellowing. The lower fan leaves especially. They are on day 23. Not sure if its overwatering (it's been taking about 4 days for the 5 gallon air pots to dry out). Or nitrogen deficiency? I've been feeding Advances nutriance ph perfect at about 1/4 strength. With a small amount of calmag at the last feed. About 400ppm total. Any ideas? Yellowing with a couple of grayish spots.