Sudden Brown Spots & Yellow Leaves - Help!

[Narkgrowop]

Hey guys, so I did a flush last Friday (using fox farm soil and they recommend a flush after week 4) and both of my plants are looking awful. One of the plants has had issues since week 2 and I haven't been able to sort it out. The leaves have been turning brown, drying up, and falling off. My other plant looked amazing until the day after my flush. The lower leaves are all turning yellow, and a bunch of leaves are showing brown spots. Any help is greatly appreciated.

What Strain is it? Northern Lights Auto
Is it Indica, Sativa or Hybrid? What percentages? Indica dominant, 80%/20%
How Many Plants? 2
Is it in Vegetative or Flowering Stage? Flowering
If in Flowering Stage... How Long? Week 1 for smaller plant, week 2 for larger
Indoor or Outdoor? Indoor
Soil or Hydro? Fox Farm Soil
If Soil... What is in your Mix? 70% fox farm soil, 30% perlite
If Soil... What Size Pot? 3 gallon pots
Size (Wattage) of Light? How Many? ONe 600w LED
Is it Air Cooled? Yes
Temperature of Room/Cabinet? Temps range from low 70s to upper 80s
RH of Room/Cabinet? 25%
PH of Medium or Reservoir? Watering PH: 6.7. Runoff PH: around 5.9
Any Pests? No
How Often are you Watering? Every 2-3 days
Type and Strength of Fertilizers used? Using big bloom and tiger bloom at 5ml/gallon
Size or Square Footage of Room? Homemade tent. 20"x30"x 60"

Smaller plant:

Larger plant:

 

[daTenshi]

That looks like a Calcium(Ca) deficiency.

Here's a direct quote from the first post you get when using the search function.

Problem: Calcium is an important nutrient which helps provide structure to the cannabis plant and helps it withstand stress like from heat. A cannabis calcium deficiency can sometimes be difficult to diagnose since calcium deficiencies are often accompanied by magnesium, iron, and/or other cannabis deficiencies.

Calcium moves relatively slowly through the plant (it is a semi-mobile nutrient), which means it tends to "stay put" after it's been given to a leaf. It tends to show up on leaves that are actively growing and getting some amount of light.
Calcium deficiencies most often show up in the following places:
Newer growth (upper leaves)
Parts of fan leaves that have been exposed to the light
his lower fan leaf is mostly in the shade, but the calcium defciency appears near the edges that are getting light. Calcium deficiencies often show up on parts of the leaf that are still actively growing.
Calcium Deficiencies Appear on New or Actively Growing Leaves

Calcium deficiencies tend to appear on newer or growing leaves, which means calcium deficiencies first appear on leaves where there's rapid vegetative growth.

Some of the most noticeable signs of a calcium deficiency will appear on newer or growing leaves which may display:

Dead spots
Crinkling
Spotting / Mottling
Small brown spots
Stunted growth
Small or distorted new leaves
Curled tips
Leaf die-off
Affected leaves may appear dark green besides the spots
Other Symptoms of Calcium Cannabis Deficiency

If a cannabis plant is affected by a calcium deficiency for too long, it may begin to show the following symptoms due to the lack of calcium.

Stems become weak or flimsy and may crack easily
Stems become hollow or show inner signs of decay
Plant does not stand up well to heat
Flowers/buds do not develop fully, or development is slow
Roots appear weak or under-developed
In severe calcium deficiencies, parts of roots may even die off or turn brown
Roots are more susceptible to root problems like slimy root rot
Cannabis tends to like high levels of calcium, so it is unusual to feed too much calcium when using normal amounts of nutrients and/or regular soil. There are not many known cases of cannabis calcium toxicity (too much calcium), however too much calcium can cause the plant to lock out other nutrients, so it's important not to go overboard..

Calcium deficiencies are more likely to appear when...
Grower is using filtered or reverse osmisis (RO) water to feed plants - the amount of calcium found in tap water varies, but some tap water has enough calcium to prevent calcium deficiencies
Growing cannabis in hydroponics with nutrients that don't supplement calcium or when growing in water that has less than 6.2 pH
Growing cannabis in coco coir that hasn't been supplemented with calcium or below 6.2 pH
When growing in soil or soilless growing medium that hasn't been supplemented with calcium (usually from dolomite lime) or is acidic (below 6.2 pH)
Too much potassium can also sometimes cause the appearance of a calcium deficiency
Outdoors - calcium deficiency is more likely to appear in acidic soil (below 6.2 pH)
Different strains of cannabis tend to have different nutrient problems. Some cannabis strains (or even specific plants) tend to use much higher levels of calcium than others, and so you may see calcium deficiency problems with one plant even when all the other plants (which are getting the same nutrients and environment) aren't showing any signs of deficiency.

Solution For Calcium Deficiency in Cannabis
Your cannabis plant may show signs of a calcium deficiency if the pH at the roots is too high or too low. That is because when the pH of your root zone is off, your cannabis cannot properly absorb calcium through its roots. Therefore the first step is to ensure that you have the correct pH for your growth medium
Please note: After a calcium deficiency is cleared up, the problem (brown spots and unhealthy new leaves) will stop appearing on new growth, usually within a week. Please note that leaves which have been damaged by a calcium deficiency will probably not recover or turn green, so you want to pay attention to new growth for signs of recovery.

In soil, calcium is best absorbed by the roots in the 6.2 - 7.0 pH range (in soil, it's generally recommended to keep the pH between 6.0 - 7.0, but calcium specifically tends to be best absorbed above 6.2)

In hydro, calcium is best absorbed by the roots in the 6.2 - 6.5 pH range (in hydro, it's generally recommended to keep the pH between 5.5 - 6.5, but calcium specifically tends to be best absorbed above 6.2)

If you suspect your growing cannabis plant has a calcium deficiency, flush your system with clean, pH'd water that contains a regular dose of cannabis-friendly nutrients that includes calcium. This will remove any nutrient salts that may be affected the uptake of calcium and help restore pH to the proper levels..

To supplement with extra Calcium... (it's very rare to give a cannabis plant too much calcium, however, too much calcium can lock out other nutrients so don't go overboard)

Calcium, magnesium, and iron deficiencies often appear together in cannabis. Many growers decide to purchase some sort of Calcium-Magnesium (often called Cal-Mag) supplement for their grow room in case this common deficiency appears.

Listed below are common cannabis Calcium supplements, along below with some general information about each one. After supplementing with Cal-Mag and correcting the pH, you should expect to see new healthy growth within a week. Remember, the old leaves will probably not recover, but new growth should be green and healthy.
Botanicare Cal-Mag Plus is a calcium, magnesium, and iron plant nutrient supplement. General application is to mix 1 tsp (5ml) of Cal-Mag into each gallon of water. I have used Cal-Mag Plus several times with great results.

Guaranteed Analysis: Nitrogen (N) 2.0%, Calcium (Ca) 3.2%, Magnesium (Mg) 1.2%, Iron (Fe) 0.1%
Derived from: Calcium Nitrate, Magnesium Nitrate, Iron EDTA

Dolomite Lime - For Soil Growers (Organic)
If you're looking for a way to supplement calcium in your organic or soil setup, I highly recommend a product called "Dolomite Lime."
Dolomite is a good source of calcium and magnesium and can be mixed with your soil. The great thing about dolomite is it works slowly over the course of a few months.

Dolomite has a neutral pH of about 7.0 and will help keep soil at the correct neutral pH range which is optimum for cannabis growth.
You can buy Dolomite Lime online, but with shipping it's almost always waaaay cheaper to pick up a bag at a home improvement or gardening store such as Lowes, Home Depot, gardening centers, etc. If possible, try to get a finer grade of dolomite compared to something that is more coarse.

How to Use Dolomite Lime for Cannabis: When growing cannabis indoors, add 6-7 teaspoons of fine dolomite lime to each gallon's worth of soil. So if you're mixing enough soil to fill a 5 gallon container, you want to add 30-35 teaspoons (about 2/3 cup) of dolomite lime to the mix. Mix the dolomite lime and the dry soil thoroughly, then lightly water it with water that has been pH'ed to 6.5. After getting the soil wet, mix the soil well and wait a day or two to let the soil settle before checking the pH and adding plants. When growing in an outdoor garden, follow the dolomite lime manufacturers instructions.

Leaf Color:
Brown or Dark Spots
Mottling / Mosaic Pattern
Leaf Symptoms:
Upper Leaves / Newer Growth Affected
Leaf Edges Appear Burnt
Leaf Tips Appear Burnt
Leaf Tips Die
Yellowing Between Veins
Spots
Mottling / Mosaic
Slow Growth
Twisted Growth
Abnormal Growth
Plant Symptoms:
Weak Stems
Slow Growth
Twisted Growth
Root Symptoms:
Brown
Slow Growing
Other Symptoms:
Buds Not Fattening