Seedlings Have Brown Tips. What is going on???

hi there. i am having a problem with a plant that is only still under two inches tall. Dont get me wrong, i have grown before and come out with a good crop. Okay, this litle plant has been growing for only four days now and it is nice and short and already with a 3 paired leaf and starting on its third node. doing pretty well growth wise, but i have noticed that there was a brown tip on the first set of leaves. it has not yet affected the other leaves, and im hoping it doesnt. i am using a dilute solution with distilled water of organic liquid seaweed and tomato feed. also perlite, vermiculite, and compost, whilst a 400watt hps is blasting away. maybe it is getting too hot in there, or too many nutrients, or overwatering, so many things, but i dont know what it is! please, somebody help!
Also the light is pretty far away (18inches) , im using a propogator tank and jiffy pots that you later plant into the main pot, watering once a day with dilute solution, although i have been using a 1l bottle to feed them, and there were specific instructions for both nutrients to dilute them in 9l and 4.5l of water, i accuratly poured the minimized solution into a one litre bottle, and later on diluted it. so i dont think its a overnuting prob? any one got any ideas, please tell me.
thanks

Why are you feeding them any nutes at all? Most soil has all they will need for a good amount of time. No need to be feeding them at all this early. Did you start them with the 400 watt hps or did you use some other light when they first sprouted? Could have burnt them with that light straight out the soil? Just my 2 cents.

I'd say overnuting. shouldn't feed so early. I always start mine with an HPS and they don't get burnt.

At 18 inches from your seedlings. I have alwys been told start at more like 36 inches away maybe further away for such young plants.

thanks for the info. i will lay off the nutes then i guess, and raise the light a bit. but the new growth seems to be green and healthy still. maybe it adapted to nutes alrwady?

another question here... what is the earliest you can generally put a plant into flowering?
i need to do this due to space.

You can flower straight from seed but your are only decreasing your yield. I had a situation where I vegged 2 plants for 5 weeks and one plant for two weeks. The 2 plants that vegged 5 weeks nearly tripled the yield of the other. Just bend them over and tie them down. I did this to mine and they are only 2 feet tall and ready to pick. Probably 1-2 ozs( yielding.)