Yellowy green leaves and brown marks underside of leaves. Help!

Hey there!
 
I have a different issue with another variety of chili. Again, this is a plant I bought locally. The leaves are yellowy/green and don't look very healthy. They also seem to curl upwards at the edges and have very fine webbing on the underside of the leaves along the middle vein. The leaves also have brown patches on the underside of the leaves, often where the webbing is. Is this a fungal infection or evidence of mites? I have checked many leaves for evidence of mites (and even bought a magnifying glass!) by tapping the leaves on white paper, but I have seen no bugs. I don't think the cause fertilizer deficiency as I have fertilized fairly often with NPK, Mg, Ca etc.
 
The plant is rather tall and spindly. I removed a lot of the lower leaves as they seemed very unhealthy. Additionally, some of the leaves seem a little deformed and new growth seems to have stopped. It is the rainy season here in Indonesia so there is a lot of rain and not too much direct sunlight, which of course could be affecting things, but the plant was that colour when I bought it. I also have another plant or two that has the webbing and brown patches on the underside of the leaves, but the leaves seem much greener.
 
What could cause webbing and brown patches on the underside of leaves?
 
 

Too much moisture in the soil and in the air, because  that looks like some kind of mold/fungal in the leaves.

You need cheap microscope like this.  it's only < $3 USD.
 

 
 
some bugs are too small.   The magnifying glass?, Useless!!!
e.g. this mite
 

You only need 30x or 50x loupe to see tiny bugs clearly if you have a good eyes, there is no need for that cheap no good microscope.

Ok I'll see if I can find a loupe or a cheap microscope - whichever is cheapest. If there is still no sign of bugs, then I guess it's a fungal infection. Thanks for the input.

Chilidude said:

You only need 30x or 50x loupe to see tiny bugs clearly if you have a good eyes, there is no need for that cheap no good microscope.

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I own 6 of those microscopes. They work excellent.

I also have 2 loupes...I don't care for the loupes not as clear of an image imo. I don't even use them anymore.

Masher said:

I own 6 of those microscopes. They work excellent.

I also have 2 loupes...I don't care for the loupes not as clear of an image imo. I don't even use them anymore.

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I have one cheap microscope too, but it is no good for me. I also have this illuminated 30x-21mm metal framed glass loupe, that i ordered from China and it it is really good for the price.

I have a cheap microscope that hooks to your tv or computer, if I remember correctly it worked pretty good