Hello
I have little experience with nft but maybe I can help. First I have to ask you a couple questions. What material did you start your seedlings in? Also how did you grow them up to now, what method did you use? Can you tell me if you are useing sunlight or HID lights? If you can answer these questions I may be able to help you out or maybe someone else will.
If you are useing rockwool then I suggest waiting till the roots come out of the cube and are growing rapidly(but not too long). Also with longer roots the plant will be growing faster if conditions are proper. That would be a good time to put the seedling in the nft.
In my experience nft requires more work and can also be more difficult than other techniques. If you do it well you will get really high yeilds. Answer these questions for me and I will reply.
Amar

Hi Amar
I started them in Rapid rooter plugs. under a 1000 Watt HID. There currently about 4 inches tall and have there first set of real leafs.
Thanks Dennis

Hello Dennis
Last night I was writing a response and a huge storm came through and I lost power the in my area. I wrote a huge post and then I lost it all. Lets try again.

First of all I want to say that you don't need that light for seedlings. A light that powerful is best for more established plants. May I recommend useing a compact flourescent bulb (cool bulb, try the higher wattage ones) from your local hardware store and some lamp cord and a socket. Make a reflector useing cardboard, aluminum foil, and a glue stick.

I would use this for starting seedlings. The plugs that you use are my favorite brand and will be great. The plugs will be under that compact florescent where they will grow more compact and when they root out put them in the nft under that massive light bulb.

Here is a method which you should try. You will need the following: A container with a lid (bucket, storage tote, whatever just make sure it has a sturdy lid), buy some 2" net pots(pretty cheap), an aqurium air pump, bubble curtains or airstones(make more bubbles when attached to the pump), some line for your air pump, and of course those plugs. All of this is cheap and airpump bubble curtain and tubing are aquarium supplies.

First you make sure your container is deeper that 10" and it's size should be decent size. You take the lid and make holes that are slightly smaller than 2". The amount of holes to make should be the same as the number a plants you want to start it's better to make a couple extra. Make the holes an inch or two apart.
When you make all of your holes you will put the 2" net pots into them. The net pots should fit in the holes when pushed a little so they are sturdy.

Now you have a lid with a bunch of net pots in it. You want to fill your container with water. Your water level should be 1" below where the net pots are when the lid is on.

Also in the water you want to have those bubble curtains which are the length of your container. You need them to be the length of the container and they need to be spaced about 4" apart to ensure even coverage. Connect some tubing from the air pump to the bubble curtains. You have to drill enough 1/4" holes in the lid to let the air pump tubing in the container.

So now you have net pots in the lid and small holes for tubing you also have water in your container and the bubble curtains are inside the water.

When you plug the air pump in you will notice that the water is bubbling profusely and the bubbles are coming from all areas in the water. Also you will notice that the bubbles reach the top and make tiny splashes. Many bubbles equals many splashes. When you put your lid on the container and wait for a little while then take it off you will see the lid is wet.

Now put the lid on and put your moistened seeded plugs in each net pot. The plug will stay wet and the moisture will come from all directions. The water is very oxygenated and also evenly distributed. This makes roots grow like crazy in your new system. Use the recommended hydroponic fertilizers and this will give you healthy plants.

My plugs have roots coming out of every side going every direction. Plants in well established plugs can grow very long roots (2-3 ft). You don't need roots that long but this system will help getting healthy plants for your nft.

I tried this system because I do not like watering them in the tray that they come in and the roots grow a lot faster in this system.

I hope this helps. Let me know if you have any more questions. I would like to know how this turns out.

I germinate tomato seedlings in rockwool cubes:

and then when they are about 2" tall I transfer them (still in the rockwool cubes) into plastic cups filled with clay pebbles and put them in a small ebb & flow box under flourescents:

thanks