What is the temperature?
What is the humidity level?

Assuming there isn't any disease, and your sure the seedlings aren't over watered suffocating the roots (quite common problem with rockwool). My first thought is that 60 watt cfl grow light is insufficient. Causing the seedlings to stretch up towards the light, then the small thin underdeveloped stems just can't support the weight. Low humidity will even add to that problem, as well as could be just as bad by itself depending on how low the humidity is.

check your water - if its tap water, that could be doing it. Do you have access to pH and EC meters? If so, test your water. I would use distilled or ionized water only

RoboGeek
Why would suspect the water supply? Unless you were suspecting pathogens, but that's why mentioned "assuming there isn't any disease." pH has never been a problem with my seedlings. Given I use RO water, but still the pH fluctuate anyway. Also what good would an EC meter do? It wont be able to detect pathogens, or tell if there's an excess of any particular mineral in the water supply. I have never used anything other than RO/tap water to sprout seeds, and with the exception of spinach, I get a very high success rate.

The problem is you didn't wash out the rock wool in one and the other is using the wrong medium. The hydoron or what ever their call isn't meant to use that way. That growing system is for soil or close compact medium. If you use Perlite inbetween those clay balls things will improve. They're lacking air. Just remember what system uses what material.