Hydroponic growing problems... NEED HELP!

Hello ya'll, this is going to be the first time growing hydroponically. I have just had my first successful grow in soil and would like to get into hydro. I am already running into some problems. I germinated my two seedling and put them into starter cubes and water them with PH'd water every other day and keep them under a humidity dome. Its been about a week since they have been in the cubes and have seemed to have stopped growing. One of the two seedling is starting to turn yellow and the to inner leaves have turned black. What is going on?! should I begin adding some seedling nutrients I have? please help, I have already lost four other seedling previously in rockwool and dont want to lose these ones. Pictures can be viewed below.

Thanks

I have two possibilities Rock wool too wet~
could be caused from once a seedlings is
sprouted and are above ground and the
shell has fell off they don't need to be in
a humidity dome?

Seedlings have enough energy in them to get at least to the first set of real leaves. Do not feed them. Keep the rockwool moist but not soaking wet. Let the roots pop out the sides and bottom before transplanting/plugging them into larger rockwool cubes. Keep the light cycle constant and make sure there is no light leak during dark times.

Seedlings hate nutrient, and they hate shock. Shock will kill an otherwise healthy seedling.

What its main task to accomplish in the first couple of weeks is not folliage as many believe but roots. Once the roots are established the foliage will follow.

Feeding them and/or playing with the root area/cube will shock the root area, shock will stunt their growth.

The biggest killer of seedlings are growers who in their best efforts to correct something they think is wrong, stunt or kill the seedlings by interferring with something that has been able to survive all by itself since the cambrian explosion without human assistance.

All seedlings need is moisture (not too wet not too dry), correct light cycle, a little bit of warmth and time to establish their roots.

And always remember that growing from seed is a numbers game. Next time pop around 5 seeds (if feminized) and choose the best 2 from those to veg up - more if non-fem.