Tips are burning - need advice please

Can someone give me a hand please, this is my first attempt and i had just transplanted 3 days ago and everything is going great except for the tips on the new leaves started to turn brown and look crispy, lets go through my set up, please understand all of the knowledge i have, i have gone strictly by the book, through this site, and ready set grow. First off i have a 400w HPS system using a MH conversion for Veg, the bulb is exactly 24 inches from the top of the plant, i just raised it an additional 6inches to 30in but i dont sense a problem with distance since my hand/arm can stay at 24in w/o a problem, from the get-go i used miracle grow organic choice for the seedling until i heard of too many mixed reviews, so waited till it was transplant time to use the fox farms happy frog, i am not using any nutes yet, my PH meter(the $10 kind) is reading around 7.5-8 was at 7 before transplant,i am seeking advice before i attempt what i think is the logical move and flush with PH'd water. Temp is usually no more than 90 at top of plant and i am constantly giving fresh air from opening the door atleast 4 times a day with a/c on bringing temps back down to around 74-78 for an hour each time (i work from home so i have plenty of garden time ) i gave the initial watering the day of transplanting and i PH'd the water....i also run the lamp 24hrs since electricity is no concern for now, with a decent exhaust system on 24/7, today i am going 18/6 to bring the heat down...keep in mind the only nutes my baby is getting is whatever comes out of the bag, my soil mix goes as follows
5 gallon bucket
3 gallons Happy Frog
1 gallon perlite
1/2 gallon vermiculite
1 cup dolomitic lime (espoma)
1/2 cup myccorhizal (espoma bio-tone starter)
*used half cup of the mycc since the happy frog already contains it. *dont know if i should have added the lime since HF has lime in it.
my usable closet space is 3'x4' and i am hoping to get in atleast 9 plants.....i took a few decent pix...any help or advice on how to take control of this would be greatly appreciated, i do not want this to linger, maybe its normal maybe not, but i do want to nip this thing in the bud
this strain i got from a friend, i dont know the exact name, but i do know its an absolute killer kush, i wanted to get this one started and get my growing pains out of the way, i have White lable's White diesle, g-13's exodus and afghan mafia....i'm doing my best to keep the kush tip top so hopefully if its a fem it will be a nice mother, thanks in advance, rollitup, out of all the websites out there seems to be the most comfortable, from reading all the posts the members of this forum seem like class acts always willing to share knowledge, its a pleasure and a marvelous feeling to grow something from a tiny seed and hopefully seeing your work bear fruit

ok, last night i flushed it out, i have read that for a good flush you need 2-3 times the volume of the pot, since its a 5 gal i flushed about 8-10 gallons of PH'd water through it, i kinda had the idea to stop flushing when at first she drained dark water like a coffee, i guessed i had a good flush when it turned to a light tea color drainage, if you can let me know if i did it properely, i can already tell the effect is working since the tips were crisping up rapidly and since the flush no further burning has occured, what threw me off was that it had only been getting the nutes for 3-4 days and i really didnt know they would take effect that fast, seems to have done the trick, many thanks again CH