Brown spots on leaf edge - First grow help

[hoseb]

This is my first grow and I appreciate all the information that I've picked up here.
I started with 2 seeds:
1. Auto Berry feminized
2. Autoflower Bubble Gum feminized

My grow space is a well ventilated cabinet 3 x 1.5 x 5.5 with humidification and a humidity sensor. Lights are Mars Hydo II 400 (x2). Temps 80 with lights on and 72 with lights off. Light cycle is 18/6.

What Strain is it? - hybrid
How Many Plants? - 1
Is it in Vegetative or Flowering Stage? - auto flowering - Day 33 since sprout
Indoor or Outdoor? Cabinet
Soil or Hydro? Soil - FFOF and FF Happy frog equal parts, 1/3 perlite, 3 gal Airpot
Size (Wattage) of Light? How Many? Mars Hydro II 400 x 2
Temperature of Room/Cabinet? 72-80
RH of Room/Cabinet? 70% near plants 55% near exhaust
PH of Medium or Reservoir? Last runoff 6.2
Any Pests? No
How Often are you Watering? 3-4 days
Type and Strength of Fertilizers used? Fox Farms Grow big, tiger bloom, Big bloom
Size or Square Footage of Room? 25 sq ft

The problem is with the bubblegum plant.

The first bubblegum seed didn't take and the second one sprouted about a week behind the autoberry. I've used the same things on both. Watering with RO + calmag + ph. About 1 gal per pot with some runoff. The autoberry FF flowering nutes (1/2 strength) every other watering since the flowering started a week or so ago. The runoff on both pots was low in the 5.5 range when I started and I added lime to the top soil about 3 weeks in (1 tablespoon/gallon). Runoff has been closer to 6 (I've been using blue lab). I've been also adjusting the ph closer to 7 to compensate. I added the 2nd mars hydo light about 2 weeks ago and things really took off. I also use rotating plant stands to even the light exposure.

The bubblegum plant looks light green with some faint yellow in the central part of some of the leaves (lighter than the autoberry). The leaf in question is from the top part of the plant with plenty of light. There are only a few leaves like this. Most look fine, if not a bit pale. There are a couple yellow fan leaves down low near the bottom, but I'm assuming that is to be expected.

Things I've thought of:
1. too much light- I can turn 1 light off, but I can't raise them any higher
- the autoberry is doing great and doesn't show same issue
2. too little fert
3. ph nute lockout - runoff seems fine
4. salt buildup - I haven't flushed at all. I'm considering doing this and would like suggestions.
5. drainage issue/compact soil - the autoberry drains faster and is dry in 3 days, the bubble gum is not really dry until about 5 days and I tend to water it at 4. Same soil mix so I don't know why it doesn't drain as well.

Thanks for the help!!

autoberry - Left, bubblegum - Right

 

[hoseb]

Anyone have any thoughts? I upped the RH a little and readjusted things so I got a good RH reading right over the plants. The spots on the bubblegum remain. There are a few light colored leaves on the autoberry, but no spots.

 

[incarnate]

I'm still working on my first grow so I don't have alot experience but the one on the right looks like it might have some nutrients deficiency. Maybe nitrogen or mag.
Hope things turn out well for your grow. Those ladies are looking very foxy.

 

[hoseb]

I'm still working on my first grow so I don't have alot experience but the one on the right looks like it might have some nutrients deficiency. Maybe nitrogen or mag.
Hope things turn out well for your grow. Those ladies are looking very foxy.

Thanks for the suggestion. I've been adding calmag to all my waterings (RO) except the nutes. I've been using the fox farm schedule with the trio only and have been slowly increasing the strength with each feed. It could be I'm a little to slow to get to full strength nutes.

 

[Emilya Green]

I believe that you are overthinking the pH thing. Runoff pH is one of those measurements that really doesn't mean anything about anything. Of course the runoff pH is odd... it just percolated through all of that soil, picking up broken down organics on its way through. The reading there has no relation to the pH of the soil in your container, unless you have just done a 3x flush and the water is running out clear.

I did an experiment one time to see how much water is in saturated soil. I took a solo cup, filled it with dry soil and then weighed it. Then I carefully watered it to runoff, and weighed it again. I now knew the weight of how much water I added. Then I took an empty cup, and measured out that much water weight. Here is the picture of how much water that was:

What I found was that 2/3 to 3/4 of the volume of that cup was water! With that much water, compared to the small amount of soil that was actually in there, it makes sense why the water pH is so important... there is so much of it, that the soil has no choice but to achieve the same pH as the water that is applied. At least for that moment in time, the soil pH, has to be that of the water.

From that moment on, the soil pH is a moving target. It immediately begins to creep upward, or drift, and it is our goal to start out at the low to middle of the range and let it drift through the entire usable pH range until the next watering.

Study this chart:

When you start out at a pH of 7, your pH creeps up from there, immediately being outside of the range of 6.3-6.8 and very quickly iron, manganese, boron, zinc and copper become hard for the plant to uptake. The damage on your leaves is occurring in the upper growth, indicating that whatever is lacking, is a non-mobile nutrient... the plant can not take what it needs from the lower leaves, and again this points to the non-mobile micronutrients.

Stop worrying about the runoff pH and from now on water and water/nute at 6.3-6.5 pH and I believe your problem will immediately stop spreading. Usually I would recommend just locking on 6.5 pH, but I know FoxFarm soil, and it has a strong drift, starting out at the low range of the scale always worked best for me. Your high pH perfectly explains your symptoms however and I don't see anything else wrong with what you are doing. Once you get the pH adjusted, the damaged leaves will not repair themselves, but at least it will stop progressing.

Good luck,
Emilya

 

[hoseb]

Thanks for the excellent explanation. I was trying to compensate for the low runoff with ph adjustments in the opposite direction. It is interesting that the runoff ph was lower in the beginning when I was just using the ph adjusted water. I wish there was a more straightforward way to make sure the soil is properly buffered before starting.

 

[hoseb]

This is the autoberry today day 50. Similar spots. I did flush with 2 gal ph corrected RO water (6.5) followed by a gallon with nutes. I hope the final flowering goes smooth. Any further suggestions would be appreciated.

 

[Emilya Green]

stay the course... looking very good actually... how long until finish according to the fact sheet?

 

[hoseb]

10 weeks from seed. This being my first grow and also these being autoflowers, I'm sure my scheduling of the nutes was not optimal. I'm pushing the flowering FF nutes now and will flush again toward the end.

 

[Emilya Green]

10 weeks from seed. This being my first grow and also these being autoflowers, I'm sure my scheduling of the nutes was not optimal. I'm pushing the flowering FF nutes now and will flush again toward the end.

not long then... don't let a little die off worry you at this point then, that is what they do.

 

[Rifleman]

Too close to harvest to worry about a little yellow now. Look tasty!