sudden leaf yellowing then browning

[runcornward]

Hello, i am very new to growing and im not sure what is happening. Over the past week some of the leaves have developed a yellow discoloration in the leaf which then turns browns. The leaves that are discoloured feel dry and brittle, but the other leaves feel normal. This seems to be happening on the older leaves. I grow outside in soil. Any help would be appreciated.

 

[gbauto]

Need some more info on soil, nutes, and environmental conditions.
That's a peculiar symptom.

 

[runcornward]

The soil mix i am using is 2 parts garden soil from the hardware store, 1 part coco peat and 1 part perlite. For the nutrients I have been using a product by Amgrow called nitrosol. It has an NPK of 12-2-13 with 1.3% calcium and 7.3% sulphur. I use this once a week. As for the environment I am in a very warm humid climate, and it has been raining a bit lately. Looking at the nutes I notice it doesnt have any magnesium, but dont think these sort of symptoms could be caused from magnesium deficiency.

 

[gbauto]

Problems on older leaves are usually mobile nutrient issues(N, P, K, Mg, Zn. Cl, Mo).
I'm not familiar with your hybrid soil mix. I've read folks having ph issues using peat products.
Are the pots drying out or are they always heavy?

 

[MeEasy]

This almost looks like a generic issue the way they're turning almost white, I've seen this before and it never seems to cause any issues. On the other hand normally when it starts on the stem end of the leaves it's not enough iron