Unsure what the issue is - maybe CalMag?

First time grower here... so flying by seat of pants and learning loads. Thanks for reading and offering your expertise.

Liberty Haze (LH) germed 06th Sept 2020
Blue Dream (BD) germed 15th Sept 2020
Plants on 18/6 cycle

Images of close up to show issue are below, plus image of set-up.

Have had a pretty uneventful initial month, LH initially stretched as 2 day old with too little CF light, so put in big grow room from day 2 and it settled down. Done lots of reading / looking online and I think both plants are a little stunted/bushy and don't seem as tall as other growers plants. Ambient temp and grow light meant in first two weeks temps peaked at around 35c at hottest part of the day, but have settled down and plants didn't seem too unhappy.

Since day 10 for both plants I have been using 0.5ml per litre of Sensei Grow Part A&B and at week 4 got up to 2ml per litre when I saw start of nute burn. So did a watering with plain 5.7PH balanced water, then next watering I reduced nutes to 0.5ml per litre. Plants seemed to be OK if a little under-watered after 24 hours, so I watered again, and they bounced right back, looked great. Then 24 hours later the spots on the leaves and yellowing started to really show. A few leaves had spots (I thought it was leaf damage or light burn from water spots) but nothing major until past 24 hours.

I researched and think it may be the "night" temp is too low, causing cal/mag lockout, compounded by the 5.7PH.

Today I added thermostatically controlled heater to keep the grow room at 22c when the light is not on.

Also have an open trough with plain water in to keep RH at 50% and it works well

I also added Plant Magic cal/mag to the water and nutes for today's watering, and hoping this will improve the situation.
Run off EC today is 568 at 25c

Not sure if the heater and lower nutes + cal/mag will help? In fact I am not sure it is even cal/mag issue?

To answer the questionnaire I have seen others being asked to fill in...

How long has this problem been going on?
2 days

Are you growing in a PVC grow tent?
No, homebuilt, totally insulated & sealed wooden cabinet I made, no light leaks.

What system are you running? (DWC? Ebb flow? Aero? Water Farm? Flood Tables? and so on...)
Coco and air pots, tap water PH Down from 7.5ish to 5.7, and now 6.0

What STRAIN are you growing?
Liberty Haze and Blue Dream

What was the establishing technique? (Were the seed or clone?)
Seed in peat plugs, and then into Coco 10L pots

What is the age of your plants?
Liberty Haze almost 6 weeks
Blue dream 4.5 weeks

What PHASE are the plants in?
Veg

What Technique are you using?
LST, more by luck than planning!

What substrate/medium are you using?
Cyco Coco/Pearl

What is the Nutrient temperature?
22c

What Nutrient's are you using?
Sensei Grow Part A&B
Plant Magic cal/magne (only used once, before today)

What is the TDS/EC/PPM you are using?
avg EC in: 650 - 750
avg EC run off: 550 - 600

What is the pH of the "Tank"?
5.7 but moved up to 6.0 today

Are you sure your calibration is correct on your equiptment?
Yes - tested with Buffer today.

When was your last watering?
Liberty Haze Fri 16 Oct - morning
Blue Dream Weds 14 Oct - evening

When was your last feeding change? (ie.grow-bloom-micro-additional)
Don't know what this means but above is the recent activity I have been doing.

What size bulb are you using?
Maxibright CDM 315W Horizon Wide-Angle

What is the distance to the canopy?
0.8m

What is your RH Factor?
50% (day cycle) to 70% (night cycle)

What is the canopy temperature?
13c to 25c (do you mean the temp in the grow room?)

What is the Day/Night Temp? (Include fluctuation range)
Day cycle 25c-27c
Night cycle 13c-15c

What is the current Air Flow? (cfm etc.)
184m³/h RVK Fan with CarboAir 50 & Acoustic Ducting Extration
Inlet is passive duct through a Rhino Pro Carbon Filter 100mm 350m³/h
Room volume is 1.1m³

Is the fan blowing directly at plants?
The extractor fan isn't pointing at the plants
Oscillating canopy fan does blow over the canopy but doesn't point at any one place for long.

Is your water HARD or SOFT?
Soft - circa 7.5pH
Been drawing it off 12/24 hrs before Ph balancing and using to allow for chlorine to evap and to come up to room temp.

Has plant been recently pruned, cloned off of or pinched
Leaves have been removed for LST, with topping and a couple of yellow leaves that were underneath and touching the coco, didn't look healthy so nipped them off.

Have any pest chemicals been used? If so, What and When?
No

Are plant's infected with pest's
No

So, what is the diagnosis?

Steer course you have already changed couple things up . Flushing your coco with straight h2o Is going throw things outta wack use a weak soup instead.

I see plants that dried out to the point of losing roots and Now roots are overwatered or under oxygenated .

Watch out for that heater zapping all the rh out of the air and stressing out plants further . And 35c is almost 100f you have to get that lights on temp under control before flowering if you want a decent result

HighFlyingBard said:

Night cycle 13c-15c

Click to expand...

I'd say this is the problem. Can You possibly raise night temp to 18-20C ?

Mattbho
"Flushing your coco with straight h2o Is going throw things outta wack use a weak soup instead."
Thank you for your reply - Yes, the watering I have been doing has backed right off the nutes for past three waterings (about 5 days). As stated it has been 0.5ml per litre, which I then reduced this morning to 0.3 per litre.
The under-watering mentioned was marginal, coco remained damp-ish at 2" depth so coco didn't dry-out completely and was nine/ten days ago.
The RH after a 6 hour "night cycle" was 60% with the new heater on 22c.
The peak temps at 35c was 23 days ago, for about 3 or 4 days during a warm spell, but the RH remained circa 50%. So not really concerned about that anymore as I'm tracking temps and RH and it is stable during day cycle at 25c and 50% RH and plant was OK throughout this.
Thank you for the reply though.

wiesiekborowski
"I'd say this is the problem. Can You possibly raise night temp to 18-20C ?"
The new heater has run it's first night cycle and after 6 hours temp was 22c and RH was 60%.

UPDATE
Looking at it tonight after 10 hours since last checking it I think it is looking more like nute burn/lock out. Just tested the run-off from this morning's LH watering and it was as follows:
EC 1660
Ph 5.7

From my understanding the EC figure is too high and this may be causing nute burn again, so should I now run a VERY weak nute watering when it is next due? I think I need to go for something like 0.1ml per litre just to trickle some nutes in but try to allow some of the over feeding to be flushed with the waterings. Does this sound reasonable Mattbho?

Once again thank you for the help and advice.

If you switch to RO water you will have a better grow with a lot less problems. Tap water is full of stuff that isn't very good for plants. They put a lot of stuff in there for people and not plants. Chemicals are added so the pH is disabled to keep from leaching metals into the drinking water. Plus Chlorine and Chloramine are added to kill the microbes. Chlorine will evaporate but Chloramine will not, and that's a problem for microbes. You can grow using tap, but it's not going to be as good as using clean water. The problem with using tap is the stuff that's in it, blocks the receptor sites that the Sensei Grow Part A&B would attach to. Your plants will have problems from not locking on to the important nutrients.

Someone correct me if I'm wrong but HighFlyingBard is using Sensei Grow A&B but should be using Sensi Coco grow A&B. Thats probably why plants are showing calmag deficiency.