Nute burn or heat stress?

[Kaimelar]

I'm new to this, this is my first time growing. My english is not perfect either. I really appreciate the help. Thanks.

Indica/Sativa hybrid, don't know percetages. Strain is called Pure AK (feminized).
4 plants.
Vegetative.
Indoor.
Soil. Mixture of coconut hair, perlite and soil, not sure what the mix percetage is, as it comes ready for pot.
Pot size is aproximately 1.5 liters.
400W metallic halogen, 1 lamp.
Currently installing a cooling system.
The plant is in an attic and it can get pretty hot (on a hot day, up to 31°).
PH of Medium or Reservoir? I don't know. I still haven't bought anything to measure ph, low on cash.
Any Pests? Not that I know of.
How Often are you Watering? I water every 3 or 4 days. I put my finger into the soil and if it's dry 4 cm down, I water, with 200-250ml each one, which is enough to leave it moist with no excess on the platter .
Type and Strength of Fertilizers used? I'm using biogrow at 0,2% concentration (2ml in 1 liter). I'm using it once every two weeks, as suggested by the grow shop owner.
Size or Square Footage of Room? Not sure. I'd say 4 grown men fit inside.

Photos:

 

[Kaimelar]

Oh I forgot, they've been in vegetative state since 11/09/12, so almost a month now.

 

[ChesterC]

If you're getting up to 31c and only fertilizing every two weeks it's probably heat related ... they still look pretty darned healthy to me ... nice looking soil too ....I'd say it's time to use a much bigger pot ...

 

[Kaimelar]

Oh great, that's good to hear. I installed the ventilation system today and the temp dropped two degrees immediately, so I'm hoping it won't be rising to 31° again.

Should I wait untill they're completely dry before repotting? That would be in about two days. I already bought some nice big pots and a whole lot of mix for them as well.

Thanks for the reply!

 

[Jimmycricket]

Better closer, clearer pics would help.

But those white dots look more like thrips or spider mites.

 

[Smokemupm8]

Well agree with Jimmy, but i had these lighter circular shapes on a few leaves and it wasnt spider mites, maybe just a slight nute prob as it soon rectified.. I wouldnt go adding too much nutrients to it atm,as this may lead to further probs.
So just water with PH d water, and avoid foliar feeding in the direct light as it may magnify the water beads and cause similar pattern whitish spots.. Goodluk, Smokemup..