Tiny brown/copper dots

[haarish007]

Hi !

It's actually my first grow. I live in a tropical country. I normally leave my plant out during the day but provide them with additional economic lamps for about 5 hours after a 10 hour in the sunshine. Recently I've noticed that one of the lower leaves had a couple of tiny brownish copper spots. It has spread to other parts of the leaf and to other leaves as well.

It would be great if you could advise me whether this is due to some nutrient deficiency, due to some pest eg spidermites or the fact that I'm giving additional light to the plants due to using economic lamps.

PROBLEM:
Tiny brown/copper dots which initially start with one and then propagate throughout the whole leaf. Initially started with just one leaf but now seems to propagate to others as well.


Additional details:
Medium: Soil
Type of soil: back garden soil mixed with cow manure
Indoors or outdoors: remains in tropical sunlight from about 0700 to 1800. Thereafter remains under 20 W(equivalent to 100 W incandescent) economic light from 1800 to 2300
Strain: nothing in particular
Age of Plants: 3 weeks
Type of lights: Sunlight + economic lamp hung about 10-15 cm from plant top
Type of plant: indica
Watering frequency: Every 2-3 days after soil is comparatively dry normally 4-5 big spoon full
How much and when fed with nutrients: None so far
PH: unknown
Grow recipient: Small plastic cup with volume approximately 25 cl
Temperature: Tropical
Insects: possibly tiny black creatures…very tiny…smaller than a dot…seen only once.

Hope the additional details help !

Thanks