leaves browning picss new grow help please

Hello all, first time grower here unexperienced and i ran into a big problem, plant looks liek poop leaves are browning out canoeing upwards and dying.
leaf ends either turn yellow or brown while the middle of the leaf (or veins) remains green. Fan leaves were hit first, but now leaves surrounding flower are starting to suffer from this, the ph still has to be measured im am unsure what the ph of the soil is.
Growroom Specs:
Temp 12-21 degrees Celcius (lights off lights on)
Hum: 12 hours 50% 12 hours 70% (lights on lights off)
Last used BC bloom reccomended amount for 50 liters diluted in 60 liters instead, recent watering with tap water
Lights are 18 inches away from plants at its nearest point,
please help me out, im afraid im gonna lose some fine bud!
What is your diagnosis?
Here are some pics!
http://img30.imageshack.us/img30/5359/001xk.jpg
http://img121.imageshack.us/img121/9619/003umt.jpg
http://img514.imageshack.us/img514/847/005qb.jpg
http://img15.imageshack.us/img15/5098/007ue.jpg
http://img121.imageshack.us/img121/3027/010as.jpg
http://img3.imageshack.us/img3/8650/011frl.jpg

Thanks you in advance

Looks like a nute burn to me

If you have not flushed I would do so right away

looks like a ph problem, or a mg defficancy, or nute burn, do you foiler feed?

I would flush, check ph, mist some mixed up epsom salt under and on the leaves. and even chop off the really bad looking leaves.

I am having a very similar problem.....this is what I have determined for my particular case..
I have four plants...3 weeks into flower...20 litre pots...
The problem I believe was that one of my containers was sitting directly on the floor and the other three were raised off the floor about 30 cm. The soil and container on the floor was much colder than the three that are raised.
The one on the floor is the only one having a problem similar to yours..severe canoeing and browning evenly throught the leaf... All of the plants are the same...same nutes for each one...
This is just an observation...Im just a noob trying to get to the same place as everyone else.

i agree with the nuteburn. time to flush it out

Nute burn.
Too much "BC Bloom" ( 1-4-7 ), probably toxic levels of K.
Try using it every other time or every third time, with watering in between. But flush at least twice and wait for the leaves to stop getting worse before any more nutes.