Here's a little more detail on my HLG 650R in a 3x3 tent:
For veg until 2 wks before 12/12, I run at 28-29° C and 60% humidity. Humidity goes to about 55% prior to 12/12 but is measured with the probe slightly within the top leaves. You want to monitor what the plant is feeling. Probes not in the canopy register much lower levels. 2 wks before 12/12 the temp steadily drops to 20 22° C at 2° per wk.
I'm in week 7 now at 30" above plant and at 535 watts and the plants are very happy. I usually grow 1 or 2 plants and veg 8 wks but these plants were in the cold & under a small light for the first 5 wks and are much smaller than usual. They are growing quickly now. I have back problems so fewer plants is easier for me.
For flower I try to get to full power at about 22 inches but it depends on the strain and how healthy they are. I get a little bleaching but I'm more concerned with getting max photons deeper into canopy and am willing to sacrifice a 1/4 inch of the center flowers to achieve that. I smoke the white tips and they seem fine to me. Sometimes I have to turn down the light but can usually keep it at full or close to full power.
I don't supplement CO2 but ambient in my basement in winter is over 800 ppm most of the time so I have a little bump there. I have five 6" non-oscillating fans in my tent to ensure that no leaf is robbed of air exchange. 4 on top and 1 on bottom. I will add a sixth one on the bottom soon. Just strong enough to not have wind-burn. This helps with nutrient (calcium) uptake. I also foliar spray calcium chloride twice a week or so. I avoid calcium nitrate foliar because the N can promote growth increasing the demand for calcium.
Current fertilizer is Jack's 5-12-26 with calcium nitrate. I often mix my own using Hydrobuddy. At week 7 of veg I'm at an EC of 1.8 fed 5 times per day. I try to run with only nitrate nitrogen but if runoff pH goes high, I'll use a little ammoniacal nitrogen. This run I mixed a little Sulphur into my 70/30 coco/perlite mix to keep ph low and it seems to be working. 2 grams per 3 gallon air pot. pH started to rise and then 6 wks later started to drop keeping it within range. The other plant is a bit stunted because of the cold start so not using much nitrate so it's having the opposite problem of low pH.
I've struggled with calcium in the past but so far with lower humidity, nice vibrant green plants. Flowering is the real test but based on what I'm observing and the fact I've tried everything else, I'm pretty confident that they will finish well.
The extremes that I'm pushing (light & temp) are the reason I was having problems and could have just turned the light down. But when it goes right, the buds just sparkle and the effects are much stronger. Look up Mitch Westmoreland environment study. It's preliminary work but my tests indicate it's rock-solid. Both Mitch and his mentor, Bruce Bugbee are currently saying that temperature is the best method to crop steer cannabis. I just bought a much bigger AC unit than you'd think I'd need so I can maintain the low temps for a longer grow season.
I attached a photo but the camera makes the plants look a paler green. The are a little greener than they look but not dark green.
As Bruce Bugbee likes to say, not everyone can drive a car at 300 mph but it sure is fun when you can. (paraphrased slightly)
Here are some other things I've tried to correct calcium deficiency:
Solutions
- Twice a week foliar spray calcium chloride @ 400 to 800 ppm & pH 5.8
- Reduce N in solution
- Reduce ammonium N
- Reduce EC of solution
- Turn down light
- Reduce humidity to increase transpiration
- Reduce the K:Ca ratio if it's high. (e.g. 3:1 to 2.5:1) to reduce competition for Ca
- Defoliate - don't remove many, only want to remove microclimates to promote transpiration in centre
- Add fans - this is important!
- Blow air up directly into center of canopy from bottom of plant