grow in humid country

hi,
as you can imagine by name i'm a newbie in this I live in a very humid country and I tried my first grow...wich was close to a disaster ( less than half an ounce per plant).

Here's the set up :
3x 600w HPS
32 pots (quite big about 10liter)
soil is coco
blue cheese seeds
nutrient house and garden
air extractor
temps are quite high between 27-31 celcius, for that i need to open the air con almost 24h
humidity between 55-75
problems I encounter:
first the plants started to stretch, this is because i think i didnt use MH for the vegetative ( i will change for my second grow)
then plants started to be yellow leaves, first I thaught it was over feeding so i flush a bit, then i thaught it was a PH problem so i tried to lower it then again i thaught it was over feeding again...I was quite lost as you can imagine.
Everything went very slow i think, cuz blue cheese are suppose to have 60 days flowering and I harvested mine at least at 75-80.
So what you guys think? Is it possible to grow in very hot and humid country ? Do you think all my little mistakes add up and thats why i got such a poor yield?
also when I dried it, it turns really dark green almost brown and the smell is not nice ( maybe the humidity is also a problem there??)

THanks for ur help!!

Yellow leaves could be a sign of N deficiency, as for drying, sounds like you got mold 'cause of the high humidity, an other thing, just 'cause the breeder says it will be done in 60 days that's just in optimal condition, go by the trichs next time not the breeders advise.