first, you should plant them about 1/4" deep into the soil (5cm sounds too deep to me) ... also, I think your problem is wet soil ... Im just guessing you have 'damp-off' going there ... thats exactly how my seedlings looked when too wet ... start again, germinate only to where the white 'foot' just barely sticks out of the seed, they're too fragile when they are allowed to lengthen ... place 'foot' down into moist (not wet) soil ... good luck ... P.S. my opinion of water meters is "useless" or worse ,,, judge the water need by observing your plant, and poke a finger into the soil ... :smokin: