just because its dry on top the roots under the soil need to breathe also. they like to have a wet and dry period overwatering promotes root rot and stunt growth eventually death if you keep on. best way is to get a moisture meter or pick up the pot and judge by weight as to when to water. water when the pot is light
with young seedlings, use a mist bottle to keep the soil slightly damp - not wet. also, get rid of the domes. as stated earlier it is probably causing damp off. GL