Get them out from under that dome, and harden them to the real world. If you're having problems keeping them hydrated, likely a good idea to transplant into the next size container.

Waaaay too young for Miracle Grow nutrients. After the 4th to 5th internode, start thinking about half-strength doses 1/4 tsp per gallon per week, I believe) and watch for their reaction.

Soda water is a good way to attract ants and other undesirables, but your seedlings do not need the additional carbs or carbon yet.

Are you spraying them with anything? Likely you're keeping the foliage too hydrated. (possible cause of the spots)

Vinegar isn't the best, but will work in a pinch, but it's not a good long-term solution. Best to use the right tools for the job. I use phDown.

Do not overclock the seedlings. They are dying to perform, but don't push too hard. Keep in mind that growing cannabis isn't an event, it's a process. Shortcuts often breed disaster.