Some help please

i start this grow abut 8 day ago
i made some experiment:
i germinate 2 seed 1 big and 1 small and moved them to 4 inch Rookwool
the small one show some progress to but it mach slower ( i help him today to get reed off the seed shell )
the big one show good progress- the roots are get out from the Rookwool
by the way i didn’t apply any water solution on the Rockwool before using them and it is seem that the are ok.
i see that the roots are white color except one root that his ending is brown
what could it be ???
there is an option that root can be damaged from air (no light) ???

filtered water+4 drops of Rapid start
pH - 5.8
ppm: 200
humidity : 50-60
media: Rookwool

It is typical for roots to turn brown when exposed to air, and dry out.

are u watering them they look dry

Yes, if you mean the outside of the rockwool cube. Roots will turn kinda brown when they are in the air and dry out, but even as important as moisture for your roots, the roots need to be in total darkness most of the time. Root do not like light at all.

Rockwool is meant to be placed into a secondary medium in order to keep some moisture throughout the root zone. Leaving it to sit in the open air, dries the fiber more quickly and puts the root zone in danger. Yields will suffer.

The exception to submersing the Rockwool cubes into a secondary medium, would be the “Dutch” method of; “leach trays”; Whereas; There is a constant water motion along the end line of the leach trays, wicks up the necessary nutrients and water. Said trays are fitted with cotton wicks to wick moisture from the nutrient bath.

I woould get enough perlite, lava rock, or hydroton to fill that ebb and flow tray. A good bed of medium will make your life a lot easier! Peace

Latewood’s advice is great, especially as this will allow for a bigger root zone than the cubes alone, which means potentially bigger plants and more vigorous growth as well as bigger yields.