plz help same old blooming problem

Hello i.m new around these parts, i was wondering if any body could help me out with a problem. i.ve grown cannabis a few time now with same result. about half way into the blooming all is going well and the bud is coming on nicely but then i get grey spots apear on the leafs at first only the odd one of two but then it starts to take over the plant and the leafs start to curl downwards. i.ve been feeding the plants with a kp 3,12,14 mix for about 4 weeks by this stage, the water where i live is very hard and the temperture in my growing box is 35-40F. its really strange because they grow well upto this point and were really healthy.

 

First thing I notice, is your temps. I'm not sure you got the conversion correct. 35-40 F, is about 30F degrees too cool to grow mj. (32F is freezing)
next lets look at the n-p-k.(3-12-14) Potash may be too high.Too much K may be "locking out" nute uptake. MJ requires some K to maintain health, but usually in smaller proportions than nitrogen or potasium. Flowering nutes should be hi P and low in N and K. Have you tried flushing the medium to remove salts buildup?..This too, could be contributing to the failure.
next, "hard water" hmmmm. where to begin. What is the ph?..Does it have chlorine? If its city water, (chlorine) it helps to disapate the chlorine by leaving it set out for at least 24 hrs before useing it. Hrd water alone, can cause a nute lock. Might try useing reverse osmosis or distilled water to prevent it.

A few questions that would aid in the diagnosis..
How old are the plants/how big, what size pots, how often and at what rate have you fed ?

 

35-40 C is 85-105 F I use water from my fish tank for the correct PH 6.5-7.0 guess im lucky in scotland we got soft water in abundance.If you can aford a small tank=50-80Ltr=£30 you can then get (Ph up) or (ph down) from the local aquatics store its not expensive a couple of Quid. Look out for Mr Ekul le chet he stays in your area and might be able to put you in a better direction than me

 

thank guys it sound like you could just save life lol. yes temp 35-40 c and just started flushing. i leave water in my setup to age for at least 24hours then use it as and when i need by adding food to wat i use. i used to keep softwater fish so know ph buffers dont work for long because of the high gh,kh, ph is around 7.6+ mark. cant aford a reverse osmosis so was thinking of filtering throught peat.
plants kush grown from seed and are 12weeks old and in bloom for 5 weeks and 2.5 feet tall, there in 10inch pots with 4 to 1 soil and perlite mix. i feed every time i water which is every 2-3 days with just under the stated dose of food. thanks again peep..

 

'soup...I believe you will see a great improvement by lowering your temps AND your ph. Temps are ideal at 70-80 F and ph closer to 7.

 

nice one peeps i feel i.m really getting somewhere now and there.s light at the end of the turnnel. all ya advice is being put in to action we speak.