Leaves yellowing and dropping

[Bomparty]

Hey guys. I have a few nice pepper plants, but half of them have problems. They are all growing in 3 gallon buckets with the same soil and on the affected plants the lower leaves are turning yellow and dropping. They are standing in a greenhouse and the temperatures ranges from about 55F during the night and 100 F. during the day. 
Every time I water they get half strength 4-1-5 liquid synthetic fertilizer, and I water them when the soil is dry, and they start to wilt a little bit. 
 
links to pictures should be posted below 
 
https://ibb.co/wzF5Dq2
https://ibb.co/ZG0F34R
https://ibb.co/BBqTbbn
 
 
Any help would be greatly appreciated 

 

[matty]

I'm wondering if its magnesium – based on that image of the lightness starting at the tips and moving inwards.

 

[solid7]

It would be helpful if you could wrap your images in BB code, so that we don't have to click out to view them.
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Anyway, we can't just rush into a single nutrient based assessment of the problem.  You have a 45 degree temperature differential between night and day.  I can't help but think that this is affecting uptake.  But let's put a pin in that, for now.
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What type of mix are you using in your containers?
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What is the exact fertilizer that you are using?
 

 

[Bomparty]

I'm wondering if its magnesium – based on that image of the lightness starting at the tips and moving inwards.

 
I have been suspicius about that too. From my own research that is the deficiency that comes closest. But I have added a mixture of calcium and magnesium to the soil which didn't help. That's why I'm wondering if it could be something else. But thank you for the reply 
 

It would be helpful if you could wrap your images in BB code, so that we don't have to click out to view them.
.
Anyway, we can't just rush into a single nutrient based assessment of the problem.  You have a 45 degree temperature differential between night and day.  I can't help but think that this is affecting uptake.  But let's put a pin in that, for now.
.
What type of mix are you using in your containers?
.
What is the exact fertilizer that you are using?
 

 
 
 
Thank you very much for the reply 
 
Next time I upload pictures I'll try the BB code thing. I agree it's alot easier to se the pictures that way.
 
The potting soil I use is a mixture of store bought potting soil with added peat moss, and compost. It is difficult to see in the pictures as I'm using mulch.
I reuse the soil year after year and in the beginning of every season I add a bit of fresh compost to rejuvenate the soil. Maybe it isn't enough though. Should I perhaps make some compost tea to help the soil life?
But yeah the cold nights we have in Denmark sometimes are annoying,   and I have also been suspicious that it could be a problem too.
 
The fertilizer I use is not a 4-1-5 as I wrote earlier. It is a 3-1-4. It is an all round liquid fertilizer and I have been adding half strength in every watering. Perhaps thats not enough
The fertilizer components:
Nitrogen:     Urea; 0,5% Ammonium; 0,3% Nitrate; 2,0%. All water soluble. Which the P and K also is.
It contains micronutrients too. 
Hope that is what you meant. And can help further in the investigation 
[post='[URL="https://ibb.co/YZSG9vK"][IMG]https://i.ibb.co/6BS5h6p/IMG-20190702-111104-1.jpg[/IMG][/URL]'][/post]
 
Seems like the BB code thing works for me
 
 

 

[Tod]

My plants have been getting too much water due to rain, they look the same as yours.
 
Covering mine in advance of storms seems to be helping, (they're in raised beds).
 
Yours being indoors shouldn't be getting rained on but are they too wet?

 

[Bomparty]

My plants have been getting too much water due to rain, they look the same as yours.
 
Covering mine in advance of storms seems to be helping, (they're in raised beds).
 
Yours being indoors shouldn't be getting rained on but are they too wet?

 
Hi, thanks for your answer 
 
I don't think water is the problem in my case, as I only water when my plants are wilting. But my greenhouse sometimes get very warm, which can also make the plants wilt no matter how wet the soil is. So maybe I'm watering them when they don't actually need it.    Anyways I will try to let some of the affected plants dry out a little longer to see if it makes a difference. Otherwise I'm thinking that it could be the cold nights. 
I will let you guys know if I solve the problem. 
 
Btw. how warm is it in your area?