Suspected Phosphorus Problems

Hey all! So I have started a small scale personal garden of mine in my closet about a month ago. It is really low budget, but super stealth. It's more of a hobby than anything substantial. Well, I think I am running into minor phosphorus problems. I am using just some miracle grow potting soil and plant food, so it's nothing fancy. I was hoping you guys could shed some light on the situation.
A couple of pics,







As you can see, the edges are turning a bit brown, and the stems are purple. I'm not sure if the stem color has anything to do with the leaves, but I suspect it does. I have watched the browning of the leaves spread slowly over the last week or so. This seems to be a Phosphorus problem if I had to guess. It is possible that I over fertilized, but I have since removed almost all of the little fertilizer pellets. I try keep the soil lightly moist, but I never over or under water. Any ideas?

That blows, what is your setup/routine? I grew good buds in MC with there flowering food 153015 1 tsp every 5days in 1/4gallon spring water/ 5gallon buckets with good drainage. soil mix 1/4cow shit 1/2 MC garden soil 1/4top soil. watered 1 gallon between 4 buckets every morning. 1hour before the 400w hps kicked on in the 3x3 mylar chamber. 100cfm fresh air vented my op. on the ins and outs. Over all I'v had alot of nothing but good things said about my almost free 1/4 pound crop that took amost 5 months. The girls got cut at 4 1/2 foot tall. For bag seed I could ask for nothing better. I hope Yours is better than mine. Glad to help

Well, I don't really have any blend soil grow going. I probably should... It's just the garden variety of potting soil. I'm thinking of getting some organics to throw in the soil with it. Hopefully that will help. The best case situation is to figure out exactly what is going to, so maybe I can fix just that. I'm running 200w cfls with 150cfm air flow and a CO2 drip cup. I give them a light misting at least once a day, and a good watering 2-3 times a week. But damn, 5 months. That's quite a wait. I'm comming up on a month and a half so far.

so nobody knows whats going on?

did you ever resolve this problem 777nk ??? i have exactly the same problems in my garden ,

Well, I just re-potted the other day. Gave it fresh soil, cleaned out any nutrients I had added, and fixed some drainage issues. So far, the browning of the leaves seems to have stopped. I'll report back in a few more with better results.