stems turn purple then die

greetings all,,,,, I am a newbie and this is my first attempt at a grow. been having terrible success in gettings seeds to germinate.... I have a germinator with the heat pad and dome, using rockwool cubes. out of 15 seeds I have gotten 3 to sprout. on most, the seed cracked and the taproot was evident but but didn't get any longer than a quarter of an inch and didn't make it to the top of the rockwool......... The 3 that did sprout seem to be doing fine for the first 3-5 days. The first set of true leaves come in fine, then the 2nd set starts to come in and then growth seems to halt. The stems seem to turn purple around the 5th day and loses vigor from there on....
I pre-soaked the rw for 24 hrs. in ph water at about 5.3 I have them under T-5 wave floros (4) 2 feet tubes..... Haven't fed them any nutes,,,,,just tap water. don't think I am overwatering, I try to keep the cubes moist. any help, Ideals is greatly appreciated.

PH?
And it sounds like your germinating them in too much water.ket it start to dry out a bit once the seed cracks.Like you would with soil...water let dry water...but you can't let it get too dry or the seed will die.Let dry to a damp feel not dry.
The tap roots should grow to about 3/4 s of an inch then put in rockwool and wait a couple dayz.

A seed should be planted at a depth three times the diameter. A tap root is very subseptable to stress. and just be careful not to stress them in any way once she cracks
onelove
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