Too much water man. At the seedling stage they need very little water, especially in soil. Try give them less than half of that. After they begin the vegetative stage they will ask for more. A good technic to understand when to water is to lift your bag when it's dry and know the weight my muscle memory. Let the first 2/3 inches of soil dry and then water again. There's no rule about how much you have to water a plant, you have to understand what the plant is telling you. So, don't water everyday, water just when the pot feels light and the top soil seems dry. Good luck!