OK I will do that now Delps.
*Speaks to ChatGPT*
SO, results are in.
I told it my PPFD, temps, feeding EC and so on.
I also told it I want a single figure and not a 'range'
It landed on 6 ounce dry weight.
First grow in a 2x2 and in DWC so I don't know if that sounds about right, high or low.
Thoughts?
Anyway, time for my update.......
Went in tonight and topped up the water level.
Checked EC and after topping up we are sat at 1.8
Actually, here are my stats
ENVIRONMENT
Lighting at canopy: 1000umol
EC: 1.8
Temp Range (Lights on): 23.69°C to 24.31°C
Temp Spread: 0.62°C
RH Range (Lights on): 53.14% to 60.63%
RH Spread: 7.49%
VPD Range (Lights on): 1.00kPa to 1.21kPa
VPD Spread: 0.21kPa
Temp Range (Lights off): 21.64°C to 22.28°C
Temp Spread: 0.64°C
RH Range (Lights off): 55.96% to 58.57%
RH Spread: 2.61%
VPD Range (Lights off): 0.92kPa to 1.00kPa
VPD Spread: 0.08kPa
I think that's a bit low but a few comments.
The side view shows that there's a fair amount of internodal space. That's a function of the spectrum and PPFD over the life of the plant. As flower progresses, the buds tend to grow into each other ("stack") but only so much. If you give a plant a lot of light from the outset, you will tend to have plants that are shorter and have shorter internodal space. And, yes, you're at 1k now, that will give you good growth but it can't go back and reduce internodal space.
GPT gave me some valid criticism about my light levels. The light levels in the first few days caused leggy seedlings. That didn't carry over into later stages but I was surprised that giving my plants 100µmol for a new days had that impact.
Another issue, and this something that GPT pointed out to me also, is that at 1kµmol, I probably should be running a slightly higher EC. Like you, I was at EC 1.8 and 1000-1150µmol but, with that amount of light GPT advised me to go to 2.1 or 2.2.
What it's taken me a while to formulate is how light and nutrients function together. My tuppence—Light is how a plant makes food (it makes glucose via photosynthesis) and nutrients have to be given in rough proportion to the amount of light (light=food while nutrients are vitamins and minerals). That's simplistic but true, nonetheless.
The key issue that GPT pointed out is that at 1kµmol, the plant is running, essentially, at 100% so nutrient levels have to be increased to get the most out of the high PPFD.
I just never bumped my nutrients. In a nutshell, by growing at 1k±, I stepped away from the "legacy light levels" but stuck with the "legacy nutrient levels". I wasn't seeing nutrient issues but, per GPT, by being at 1.8 instead of 2.1 or so, I wasn't getting the best from my plants.
The other one of "the big three" is VPD, since that drives nutrient uptake and that's where increasing VPD from 1.2 to 1.5 over the course of flower helps ensure that more water is taken up and, therefore, more nutrients are taken up. Over 90% of nutrients are taken up passively by the roots and VPD (plus windspeed) are what controls transpiration.
You might want to revisit your RH values. A VPD of 1.0-1.2 is a bit on the low side—if you drop RH, you'll get a bit more transpiration which means you'll get more nutrient uptake. If you can, bump VPD and see how things go.
This is all just fine tuning, though. You've absolutely nailed it as far as I'm concerned (my first grow certainly wasn't this good!) and I think you'll have a good crop now and excellent results in future grows with a few tweaks.
"Future's so bright, I gotta wear shades!"
Note - this chart assumes a 1°C leaf temperature offset.
