Brown spots on leaves, leaves surling up

Hi, everyone

I'm pretty new to growing, this is my first plant and it's been under 12/12 for a month. The buds are not as huge and sultry as they probably should be at this stage - that's because I'm still waiting for my 400W HPS that I've ordered online. Meanwhile the plant is flowering under 6x25W fluorescents... Anyways, this is a "test plant", grown from random seeds I got from a friend. Didn't wanna start with anything serious and expensive But still it looks quite potent and I'm intent to grow it all the way till harvesting.


So, everything was pretty cool up until a few days ago, when brown spots appeared on leaves (on lower foliage first), then spread all the way up to the buds. Then many leaves started curling up, drying and falling.

Photo's are here: http://homepage.eircom.net/~saulelis/sick/

My soil mix is 1 part perlite, 1 vermiculite, 1 peat moss, 4 multi-purpose compost. I used an all-purpose Miracle-Grow 12-14-13 fert during veg and swithched to High Potash Feed 15-15-30 after switching to 12/12. The latter was used twice in a month of flowering period. Last time was 10 days ago.
My grow room is 6'' x 3'' x 1.6'', with mylar coated walls and an oscilating fan, temperature fluctuates 19-27C in night/day periods. The plant is living in a 2 gallon pot. I'm watering her 2-3 times a week, when the soil gets dryer 2-3 inches deep, so far it hasn't expressed no symtomps of underwatering.

I suspect this is due to high pH of the my tap water I use for watering - it's about 8 pH! But I only noticed it now, after the problem clearly appeared. So, i reduced the pH of water down to about 6 using cider vinegar and flushed the soil. Did it just a few minutes ago and now waiting for the results.

Could any of you experts out there confirm or deny my diagnosis and solution?

Thank you,

I.

 

sounds right
you could be watering too much-causing a calcium or mag def.
use i tablespoon mollasses per gallon while ferting. brer rabbit blackstrap or mollasses from a feedstore is best.
also heat stress looks like that, which gets worse with mag def.
the mollasses will bring your soil to life.
i gotta go shut down shop
later

 

tap water has chlorine...set in the sun for a day to evaporate per watering.