Seedlings need nothing but water, if you feed them you will kill them.Have a few questions here , have a 400 watt hps light kit on the way and all the other equipment needed but after searching the internet i saw a lot of people saying cooltubes are needed to reduce the heat . i have the carbon filter and fan etc ordered , will this be adequate in a 120cm x 120cm x 200cm tent ?
also when you have your seed germinated and are ready to plant is it enough to put it in a small pot to let it grow then transfer it to the final pot ?
and last but not least the watering and feeding , ive seen so many different opinions and i cant seem to find a straightforward answer. I was thinking day 1 water , day two nutrients and day 3 nothing ?
They have all the nutrients they need stored in the cotyledons, they're the two round edged leaves that you see first, they will die off after 3-4 weeks and then you could give them a weak nutrient dose, something like 1/4 strength or less and gradually increase as they grow.
What size is your fan?
Depending on how much air it can shift it should be adequate to keep your tent at the desired temperature, if you have a few quid to spare you could get a fan speed controller, it will idle your fan until the temp goes above what you have it set at, the fan kicks in and lowers temp. A 400w will produce a lot of heat.
Now if you are only venting into the same room as where your tent is the hot air will end up back in your tent so it is always better if you could vent into the attic or another room.
A seedling will do fine in a small pot , you can transplant when it outgrows the pot.
A seedling doesn't need a lot a light so if you have a few cfls they would be better than the 400w, keep the cfl's close to them to prevent stretching but be careful not to burn them.
Good luck.