what is the reason for the RO water? Have you tried with regular tap water? You may be OK using tap, I thought I needed RO and it turned out I didnt.
also, have you tried different seeds/H202 soak for the seeds?
you shouldn't need a humidity dome for seeds. unless you are in a desert or somewhere super dry
You are likely creating an environment that will allow pathogens to disease the plant before it has a chance to root well. I would try doing this with no dome, and using a spray bottle to keep the top layer of coco moist from the fans drying out the coco. After they root down you wont have to worry as much and can let the plant drink