Yellow and brown spots

A question from a fellow grower:

What causes yellow and brown spots on cannabis leaves? Started about 8 weeks into vegetation.
I checked your symptom checker about 10 days ago and it looked like I had a calcium deficiency. I added garden lime to the water for a couple days, but it didn’t seem to solve the problem. See attached.

Strain (type, bag seed): White Widow from seed.
Soil in pots, hydroponic, or coco?: SunGro Horticulture SUGRMIX4
PH of runoff or solution in reservoir?: 6.5
What is strength of nutrient mix? EC, or TDS: N/A
Indoor or outdoor: Indoor
Light system, size?: Advanced Platinum Series P300 300w 12-band LED Grow Light - DUAL VEG/FLOWER FULL SPECTRUM
Temps day, night: 75-80 / 60-70
Humidity day, night 50 / 50
Ventilation system (yes/no, size): Yes, 6"
AC, humidifier, de-humidifier?: Humidifier
Co2 (yes/no): No

So you added lime but did you try epsom salt? because unless it’s bugs looks very much like Mag def and Sungrow is a soil less blend formerly known as Sunshine Mix #4 ph should be slightly lower 5.8-6.2 I found gave me good results. Also if it is Cal issue it doesn’t repair existing damage only new growth will look healthier

The pH level also comes into play with a calcium deficiency in a hydro setup. If the pH level is outside the range of 6.2 to 6.5, you are more likely to have a calcium deficiency than if it is within this range. Flush out your system with fresh water that has the proper pH level as well as a boost of nutrients to restore the balance.

Your P H is off. You said it wasd 6.5 Should be 5.4. 5.8

Calcium gets locked out of soil growing at ph levels of 2.0- 6.4
Calcium is absorbed best in soil at a ph level of 6.5-9.1 (Wouldn’t recommend having a ph of over 7.0 in soil) anything out of the ranges listed will contribute to a
Calcium Deficiency.

Hydro and Soil less Mediums

Calcium gets locked out of Hydro and Soil less Mediums at ph levels of 2.0- 5.3
Calcium is absorbed best in Hydro and Soil less Mediums at ph levels of 5.4-5.8 (Wouldn’t recommend having a ph over 6.5 in hydro and soil less mediums.) Best range for hydro and soil less mediums is 5.0 to 6.0. Anything out of the ranges listed will contribute to a Calcium


Thanks Donaldj. Makes sense.

Thanks for the info garrigan62.

Hope we didn’t confuse you too much? it is a Cal issue it’s just your ph range is too high for the kind of medium you are using Will said it simpler between 5-6 ph and you likely don’t need to add more cal since it is present but you can mist plants with it as part of a foliar feed to speed recovery

I’ll try lowering the pH and see where we go from here.

Thanks Again,