Seedlings problem, please help me!!

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

well to me it sounds like a combination of overwatering and overnuting!u shouldnt be giving ya plant nutes everyday just like you shouldnt water ya plants everyday especially when there that young!so ease of the watering for a while and the next time you water just give um water but wait till the soils dry about 2-3 inches down!

i have always waited for the soil to dry out, but they dry out very quickly due to the jiffy pots and soil mixture. i will lay off the watering then.
also, do you know the earliest i can put it into flowering?

you can put them into flowering after they have hit 4 nodes.

It's definitley not heat. And if it's brown... it's probably not nute-burn (as you would get more yellow tips on all leaves if this were the case). Sounds to me like your roots either cannot breathe or are being over watered. As a rule of thumb, you should stick your finger in the soil... if it feels dry enough to water, wait one more day.