First grow, yellow leaves and dark brown spots on day 56, advice appreciated please

[HappyFarmer420]

Hi All,

First grow, first time posting here asking for help. I'm not sure if what I'm seeing is a problem, but I'm thinking it is. I thought it was some sort of cal/mag deficiency, and started adding calmag to nutrients yesterday, but problem seems to advanced significantly over the last 24 hours. Not sure if the plant has started eating its own leaves yet, or what.

First my setup:
Strain – Autoflowering White Widow (2) and Autoflowering Northern Lights (2)
# of Plants - 4
Grow Type – Soilless
Grow Stage – Flower, day 56 from sprout, 2-3 weeks flowering nutrients
Setup – Indoor, 5x5 Vivosun Tent, Vivosun Exhaust fan and carbon filter
Light - 800 Watt LED – Mars Hydro Pro II Epistar 160
Pot Size: 2 Gallon
Medium: ProMix HP
Nutrients – Remo, strengths are as per Remo recommendations, Remo Micro, Bloom. The Remo Astroflower, MagnifiCal, Natures Candy was started yesterday. 7.4 mL of each per gallon.
Watering: Every three days (thinking about going to every 2 days)
PPM - 850
pH – 6.35
RH - 40%
Room Temperature 74
Room Square Footage - 25
Pests - None Known

I've got 4 plants exhibiting this problem, one just started showing the dark spots today. It seems to only be affecting the fan leaves, but there are some dark brown spots on some of the larger sugar leaves in the cola. These are colored green, but have the dark spots.

I have only been feeding them Remo Bloom and Micro until yesterday. I went and bought Remo MagiCal, AstroFlower, and Nature's Candy yesterday, and watered them all thoroghly with these in the mix (also including the Micro and Bloom).

I'm hoping this is just a part of the flowering process, because it does also kind of look like a Nitrogen deficiency, which would make sense if the plant is pulling Nitrogen from its fan leaves as part of the flowering process.

I'm a first time grower, so I really have no idea what to expect, hoping some people with throw out some opinions. Sorry if I've left out any relevant and necessary details. If you have questions, I'll try to respond quickly.

I've attached the pics.

 

[improvise]

I no expert but it looks very much like nutrient burn. welcome to the community. Cannabis Plant and Pest Problem Solver - Pictorial. regards

 

[Chris Scorpio]

pH is too high for Coco

Looks burnt and some possible calmag issues too

Never run over 1/2 strength nutes till yer comfortable reading what they need, and if yer using RO water gotta use calmag. Even in tap water it's a good idea

Not sure if any of those nutes, sounds like lot better that's an issue, is a P booster but helps in late flower for sure

 

[Chris Scorpio]

If it's Coco you should water daily, some do 2x a day I think in flower

 

[fanleaf]

I see you're growing in promix HP and that is kind of my specialty LOL. I can pretty much figure out what your issue is based off of the information that you have given. Since you have these decent-sized autoflowers in 2 gallon pots if they are eating and drinking like they should they should be dry every other day at least. If your promix is staying wet longer than that this is the reason why.
Even though you are feeding them per Remo nutrients recommendations you have to remember you were in 2 gallon pots so if you have to feed them every other day you're going to want to cut your nutrients strength by at least half. If you're feeding full strength nutrients 2 to 3 times a week you're soil, or promix rather, is very salted up with unused nutrients causing some burn first along with what looks to be magnesium issues caused by many or all nutrients to now be locked out and unavailable to the plant because of the salty soil and I'm sure the pH is off the scale acidic. The way I grow all of my autoflowers in promix HP is by cutting the nutrients strength in half since you're feeding multiple times per week. Always add a little bit of calmag to every feeding and you won't have the issue nowhere near the extent that you have now. See, if they're directions call for x amount of nutrients that is usually assuming it's a one time a week feed. So that would be the total amount of nutrients needed for one week however in 2 gallon pots you need to feed and water them about three times a week if they are eating and drinking correctly so cut that nutrients strength in half or less because they will be getting the same amount of food per 1 week. Once your promix gets really salted up with nutrients the plants will usually slow their drinking down to a halt. Where they should normally make the pots dry in 2 days at the very most they may still feel wet and heavy for 5 days or more. Even though you were in flower right now you are in promix so I would highly suggest watering each plant with a bare minimum of two whole gallons of pure water while you collect what comes out of the bottom of your pots. I am almost willing to bet anyting once you collect all of the drainage from the bottom it will be a very deep brownish color. After you flush each plant out with a minimum of two gallons of fresh pure water mix up one more gallon for each plant with half strength nutrients and a full strength dose of calmag. The leaves that are very damaged will not get better but you can try to minimize the damage by doing this. Since it's promix HP you are absolutely fine to run that much water through those pots without it causing issues. So to sum it up to minimize your damage each plant needs to get 3 gallons of water. 2 gallons of pure water first , then one gallon of half strength nutrients with a full strength dose of calmag. growing in promix I would be sure your nutrient mix is pH somewhere around 5.8 or even 6.0 would be good right now and help it suck up some calcium and magnesium.

 

[HappyFarmer420]

Thanks for the responses, and thanks for the long post fanleaf, there's a lot of information in there that I will take to heart.
As a first timer, I did the research, and went forward with a set of assumptions, based on conflicting opinions that might be outdated, or even wrong.

I've been using AFN (The Autoflower Network) as a resource on Autos and Promix, but I'm pretty sure it is out of date. I was following all the recommendations made by a guy called 'Muddy' on the AFN forums.

The watering regimen I was using was to water until I had a lot of runoff (TDS around 1000, pH around 6.8, I check a couple plants every couple weeks) , and then weigh the plant. I usually a watered the plant until it weighed about 8.2 lbs, on average. Then I weigh the pots daily. When the pot weight is around 4.0 lbs (+/- 0.5 lbs), and was very 'light', I water it. I've been doing this 6 weeks, as per the "let the plant dry out until the pot is light" regimen. I've actually been recording these weights in a spreadsheet for 6 weeks. I am currently watering every 3 days, with full nutes. I got sick of keeping a schedule for each individual plant and forced them all onto the same schedule last week).

I looked around the internet trying to find out more about ProMix HP, and nute strength and watering regimens, but I couldn't really find anything consistent.

Like I say, I dove in with something of plan, made some mistakes, and am now trying to recover. So I will flush with pure, pH'd water (5.8) to get the acidity up, then water using 1/2 strength nutes with full strength calmag. Water frequently, say every two days, not letting the 'soil' dry out completely.

Got it and thanks so much for your help. Very much appreciated. I'm crossing my fingers...

 

[HappyFarmer420]

I think I've been causing the burn and the magnesium lockout due to letting the plants dry out too much between waterings. I've had another plant develop the same symptoms. So I did a bathtub trip for each plant and flushed it through with 1 gallons of half strength nutes today, pH of 5.8, and recorded the TDS and the pH of the runoff. Any plant that had a TDS higher than 1600 ppm got another gallon. I found had 5 plants with a ppm above 1600. After the second gallon of 1/2 strength, pH 5.8 water, their TDS was around 1100 +/- 100 ppm.

Something that I don't understand, the pH of the run off never changed, even after the second gallon. It was always around 6.25. Why can't I get the runoff water pH down? Is it because the promix/coco is so salted up?

 

[3fingerdSean]

when those lower leaves start blotching death it can mean a cpl things first thought is a mag deficiency. Second the plant needs more potassium. Adding a gram of Epsom salt p/gal will take care of the the 1st thought, adding a 0-0-25 dose of K will shore up the second.