Is this a magnesium deficiency?

[Haunts]

Hi everyone. This is my second grow using megacrop my first grow with it went fine but there's a few areas in my second grow where there's some yellowing with purple edges. See below photos.
I've been following the feeding calculator which tells me to use about 2g in 2 litres of water, along with 1g of sweet candy. I wasn't sure if it looked like magnesium deficiency?
Soil is biobizz light mix.
65w Quantum Board on 24/7
Temps 23C, humidity 40%

 

[MrToad]

What is the pH?

 

[Mañ'O'Green]

What is the breeder and strain?

 

[Arthur]

Going just on looks, I'd be checking the pH of the soil. As a soil breaks down, it is not uncommon for the pH to swing low, mid flower seems to be the time it pops up.
Looks like a potassium deficiency to me. But due to underfeed? Or lockout?

 

[Haunts]

What is the breeder and strain?

Strain is Northern Cheese Haze from Mephisto.

What is the pH?

Going in its 6.5.

Looks like a potassium deficiency to me. But due to underfeed? Or lockout?

I'll test the runoff soil pH, if it's high does that mean there's lockout (excess) and if it's a low pH its underfed (deficiency)?

 

[Tom Bombadil]

Strain is Northern Cheese Haze from Mephisto.

Going in its 6.5.

I'll test the runoff soil pH, if it's high does that mean there's lockout (excess) and if it's a low pH its underfed (deficiency)?

If the ph of the runoff is really low you probably have an excess of something and lockout... if its within or near 6-7 its probably a lack of something like mag or phos/potash... but Im not a professional.

Soil? Nutes? At that stage of growth the plants are usually as demanding as they will ever be... seems that is when most people run into issues..

 

[Arthur]

Strain is Northern Cheese Haze from Mephisto.

Going in its 6.5.

I'll test the runoff soil pH, if it's high does that mean there's lockout (excess) and if it's a low pH its underfed (deficiency)?

Both high and low will lock out different nutrients. Young plants tend to be happier 6.2 to 6.5 as they flower, there is an increase in need for p&k, as well as calcium and magnesium. 6.5 and a little higher seems to keep them praying to the lights.

Whether low or high, it could be either a underfeed issue, or a pH issue.

I don't test runoff. This is waste that you've pushed out of the soil.
Either a soil probe, or slurry test. 1 part medium to 1 part water you use. Let set about 5 minutes and gently test with a pH meter. I use about 2 tablespoons of each. Soil about an inch down halfway between plant and pot is best.

Should hopefully see something 6.4 to 6.6.

 

[Proph]

I see two things that may be factors. I see yellowing on the outer leaf tips, which is common with an iron deficiency/lockout.. And I see dark coloration on the leaves, which could be genetic, cold temps, or an issue with phosphorus uptake. I don't see any of the rust brown spots that you get with magnesium or potassium deficiencies.

The soil ph won't tell you if there is a possible lock out.. Checking the ppms of a little bit of run off would though. If you're feeding every time you water (which most do for some reason), there could definitely be a nutrient lock out happening.

 

[Haunts]

The soil ph won't tell you if there is a possible lock out.. Checking the ppms of a little bit of run off would though. If you're feeding every time you water (which most do for some reason), there could definitely be a nutrient lock out happening.

Interesting, I've not heard of checking the ppms of run off before. I have been feeding every water and I think I have a ppm meter somewhere. Do I go a head and feed as normal and then check the runoff or just use plain water and check? What should I be getting for the results?

 

[Proph]

Interesting, I've not heard of checking the ppms of run off before. I have been feeding every water and I think I have a ppm meter somewhere. Do I go a head and feed as normal and then check the runoff or just use plain water and check? What should I be getting for the results?

Ppms/Ec is highly important when it comes to feeding.. Too much of one nutrient can lock out others. The only way to have an idea of how nutrient rich your water is, is thru the ppm/ec. You can use plain water.. Just pour in enough to get back enough run off to check with the meter.

This is my "safe" ppm chart. I can follow this as a base and not get any kind of nute burn or deficiency. Keep in mind every plant is different. Some are heavy feeders. I've never needed to go over 1000ppms even with the heavy feeding plants. The standard way to water your plants is with the F-W-W-F schedule, which means to feed with nutes.. Then use plain water for the next two waterings, then feed with nutes again. Using nutes(feeding) every time you water can easily cause a lock out if your not watching the ppms.


Week 1- 100ppms
2- 200
3- 400
4- 450
5- 500
6- 525
7- 525
8- 525
9- 550
10-550
11-400
12-0