New to hydro need help with flood & drain

I have a few questions on the flood and drain system. I have 2 3x3 trays with my seeds going in rockwool cubes in a dome right now. Most have sprouted and are 1 inch tall. At what point do I introduce them into lighting. I will be using 2 platinum led 450s. I also want to know when to start fertilizing and at what strength. I don't want to burn my little seedlings with fertilizer. I also want to know how close to put my leds to my plants. I know with hid lights 600 watts I would probably do 18 inches, but I am going to use leds. The 450 is equivalent to a 600 w hid light. I was also wondering how frequently to flood. I was thinking 15 min every 2 hours. I will be using pots with hydroton in them and my rockwool cubes inside. Thanks in advance!

I have had terrible luck with Rockwood in flood & drain & opt' for sponge plugs instead .
A few cal will work until you get your 1st sets of leaves then you can introduce stronger light kept far away enough not to burn .

I have never used led but I do use 600 hps in my flood & drain tables, if a 600 hps is air cooled 18 inches would be ok for seedlings but once it's taller you want the glass much closer , I use clones & by week 3 my 600's are within an inch or 2 from the glass .

I use covered flood tables , 5 inch net pots & flood once an hour for 15 minutes , at about week 5 of budding I leave flooding at once an hour lights on & one 15 minute flood every 2 hrs lights off , with covered tables frequent floods are important to keep a cool root zone , warm root zones are susceptible to brown out & root slime .

Seedlings won't need any nutes at all , once you have a 6 inch plant start feeding them , ppm is highly strain dependant but I'd give them 300 ppm at 6 inches .

You WILL want to think about res cooling & keep it below 70 degrees at all times ,you want it 100% light proof as well as aerated very good , both help keep the res free of slime .

thanks for the great info. I am still not sure about lighting. I understand that when my plant is ending the seedling/entering veg growth I want to have my lights going regularly in terms of time intervals and distance from plant, but what about the lighting while a seedling? Should I water my seedling by hand or should I turn on my pumps?

I would water seedlings by hand seeing that they are in rockwool .

what problems did u have with rockwool? I got nutes that are compatible with rockwool. The grow shop by me said stuff like fox farm will clog up lines and rockwool as well. I got canna aqua.