Ebb & flow in greenhouse/natural light

[Vytas]

I am running 6 ebb and flow buckets in a greenhouse in the SFV of CA. Put clones in on April 1, using FloraNova grow. PH is between 5.5 to 6.0 usually 5.7/5.8, flow is every hour with a 15 min cycle. Water is RO with PPM of 120, nutrient PPM is 920. humidity is 60% and min temp=60f max temp=85f grow medium is ceramic beads, well flushed. Nutrient is changed weekly, checked daily.

I am starting to get downward curling leaf edges and some brown spotting, could this be due to too frequent cycling? i.e. Overwatering?

 

[Vytas]

After some research, I suspect that I am over feeding, a net PPM of 800ish is probably too much too soon. I will flush and dilute down to a net 600 or so and see what happens. I am also going to an every other hour cycle too. What do the experts think?

Btw this is my first grow since 1975...... And my first ever hydro.

 

[Vytas]

Finally got to the bottom of my problem: the PH meter was defective. It would calibrate perfectly at 7, but in 4 test solution read 6.7, thus I was acid burning the plants. Dumped the nutrient solution, replaced my RO membrane to get my base PPM down to under 20 and refilled to correct PPM and then adjusted to an actual 5.7 PH.

Btw, my clones have gone to bud after only 6 weeks: it seems that the effective light period in my greenhouse is much less than the sunrise/sunset period. This triggered early flowering, so now I am feeding with FloraNova Bloom. I think the next grow, I will supplement the natural light for an hour at the start and end of the day to get a true natural light period. It's nice to harvest more than once a season, but I want to see if the plants will get bigger with a longer vegetative cycle thus giving greater yield in the bloom cycle. Currently the biggest clone is under two feet tall although it is loaded with buds. I would prefer it to be 4 feet tall and loaded with buds.