Sick girl needs help!

Hello to everyone! This is my first post but I've been lurking while I do my first "practice" grow. I started growing almost by accident. My dealer was soo undependable and a seed sprouted in a flower box on my deck, so I planted a few more and started caring for the little babies. I vegged for about a month and then got a 400w HPS w/a cool tube. I ended up with 3 girls. Everything has been going well until a couple of weeks ago when one of my plants started to show yellow tips. I had only used nutes once, at a lower strength than was shown on the bottle(tiger bloom). The yellowing is spreading and she looks pretty sick. I have flushed her twice in the last two weeks. The strange thing is that I have another plant in the same 5gal pot and it seems to be doing well. What can I do to save my girl? Thanks in advance for any help you can give a struggling newbie! The pics don't show the yellowing as bad as it really is. The 4th pic is the other plant in the same pot. Its buds seem to be doing ok but the yellow plant doesn't seem to be growing bigger buds at the moment as shown in pic 5. I have another plant that is getting nutes and shows no sings og yellowing or sickness. I'm using ffof soil. I used tiger bloom once on the yellow girl and flushed after signs of nute burn. I only water when the pot feels real light. They've been in flower for 1 month. Any ideas???
P.S. I love this site!!!

how far on are you, in the last few weeks of 12/12 this is normal fan leafs going yellow.
how far on 12/12 are you.
and how ofter do you feed, and what.

sorry you say youve only fed once, you should be feeding every 4 days, thats why your buds arnt growing, if you have only fed 1 time.

They've been on a 12/12 schedule for one month. I thought about normal yellowing towards the end of flowering, but the other green plants seem to be producing bigger buds, this one seems stuck where it is with tiny buds. I've only fed it once since going into flower and that was when I started seeing the yellowing. I fed with FF tiger bloom and at 1 tbl. per gallon. I have another plant that gets fed every other watering and it's doing fine. Thanks for the reply!

I was told that ffof was pretty "hot" soil and I shouldn't feed for a month until the plants had used up the nutes in the soil. I transplanted a few days before going in to flowering. So you think I should feed again and not worry about the yellowing and brown spots?

More INFORMATION.. What is PPM when you watered.. Are you useing tap water, well water, or r/o water? What is PH of water when you water them, and also what is ph of run off. Did you add perlite to your soil? What are the temps while light is on?

You sure when you were told not to feed them for a month. That they were not talking about when they were seedlings?

Maybe the hydro shop assumed they were seedlings when they told me that. I'm using filtered tap water that sits for at least 2 days after filling the jugs. Temps are mid 70s during the day and mid 60s at night. I use ph down to get the ph to 6. Humidity is about 50% and I don't know what the ppm is and I haven't checked the ph run-off. The other plant in the same pot is doing fine...short but fine. I didn't add any perlite because it looked like it already had some mixed in. Like I said in the first post, I'm looking at this as a practice grow before I do one with quality seeds. This grow is from bagseed. Thanks for the help.

its only a few yellow leaves chop the yellow shit off

you shouldve put lights on it and used it as an xmas tree

Yeah, it does kind of have the x-mas tree look to it...except for the yellow leaves.