Auto Ak47brownish yellow tips

The only two that have the problem are the ones on the left. im afraid that more leaves may start doing this aswell. Anything i can do to fix this.

help??????/

what nutes are you feeding them? what ec? ak47 is a very tough plant but i think uve got nitrogen burn here is a link to some plants effected by nitrogen burn, compare your plants with these if they have the same symptons then you know whats causing it
http://www.google.co.uk/images?um=1&hl=en&biw=1366&bih=641&tbs=isch:1&sa=1&q=cannabis+nitrogen+burn&aq=f&aqi=&aql=&oq=&gs_rfai=

Get some cal-mag botonicare

those pics are somewhat similar but on my plant its the tips that are drying and curing in a little