What do you think it is

Here are 2 of my plants that have the same problem, actuallty i have about six all together that have this problem the rest are doing fine, All in the same media, just potting soil mixed with perlite an something else cant think of the name of it right now but its a mixture of soil that i got from RIU. Water about every 4 to 5 days, about a month and a half ago i added some 24-12-18, then after that is when it happened, and they have been like this ever since, I flushed them when i noticed this happening and havent done anything else.18/6 light period. like i said all of my others are fine but about six did this. So im going to by some phosphorus mixture this weekend and maybe that will help, because thats what i think its lacking other opinions would greatley be appreciated, Oh yea PH is 6.8.Thanks in advance.

looks like overwatering + lack of nutes to me. could be high humidity issue

All right heres my answers.

How long has this problem been going on? 1 month
What STRAIN are you growing? Dont know
What was the establishing technique? (seed or clone?) Seed
What is the age of your plants? 2 and half months
How long have they been in the soil mixture they are in now? since day 1
How Tall are the plants? 1' give or take
What PHASE (seedling, vegetative or flower) are the plants in? vegetative
What Technique are you using? (SOG, SCROG etc) sog
What size pots are you using? (Include how many subjects to pot) 12" Dia X 10" deep
What substrate/medium are you using? What brand of soil mixture are you using?(percentage of perlite, vermiculite...etc?) potting soil, 20% perlite
What Nutrient's are you using? bat guano
How much of each nutrient are you using with how much water? *Knowing the brand is very helpful* 1 tablespoon per gallaon of guano
How often are you feeding? only twice in the past 2 and a half months
If flowering, when did you switch over to using Bloom nutrients? n/a
What order are you mixing your nutrients? (example: veg nutes 1st, bloom 2nd ect) n/a
What is the TDS/EC/PPM of your nutrients used? n/a
What is the pH of the "RUN-OFF"? 6.8
What method of pH test was administered? Using Strips? pH pen? PH Pen
How often are you watering? every 4 to 5 days
When was your last feeding and how often are you feeding? about a week ago
What size bulb are you using? 400 watt MH
What is the distance to the canopy? 20"
What is your RH Factor? (Relative Humidity) n/a
What is the canopy temperature? 78
What is the Day/Night Temp? (Include fluctuation range) 68 night 78 day
What is the current Air Flow? (cfm etc.) circulating fan
Tell us about your ventilation, intake exhaust and when its running and not running ? it runs all the time
Is the fan blowing directly at plants? no
Is the grow substrate constantly wet or moist? always moist
Is your water HARD or SOFT? i have a resivor for distilled water
What water are you using? Reverse Osmosis (RO)? Tap? Bottled? Well water? Distilled? Mineral Water? tap
Are you using water from a water softener? no
Has plant been recently pruned, cloned or pinched? no
Have any pest chemicals been used? If so what and when? no
Are plant's infected with pest's? no

does the soil have fert in it already?

I think so, i bought it at lowes, im pretty sure it does. Im just confused because my others are doing great, not talking about the babys in the pictures, ive got a couple of others that are the same age as the defected one are.

it looks like they are burnt from too much nutrients, normally I would say flush, but if you do that you'll just release more nutrients. Some plants are more sensitive to nutrients then others, that's why you don't get prefertilized soil.

I know that they are all the same breed of plants, a freind of mine grows outdoors every year and hes been growing the same breed for years, which is where i got the seeds, anyways best thing to do is just wait it out i guess.

there are different phenotypes for each strain some are more sensitive to nutes then others.
I'm confused you fed with guano twice, but you also fed with 24-12-18 fert, was that water soluble or time release, what rate did you use it at?

The very first time i fert, it was with all pupose maricle grow 24-12-18, that was about a month and half maybe more ago"water soluble", and i told my freind what happened and he hates maricle grow, so he give me bat guano, which ive used once, im pretty sure just once, but i do know that they really like the guano. i had one plant that was growing short and slow, and i test the ph of the soil and it was 5.5, so i poured in a half a gallon of guana mix and tested the ph the next day and its up to 6.3, and she has purked up 50% more.