Looks pretty normal for a seedling in Miracle Grow. Every time you water, you are releasing some of the nutrients into the soil, which the seedlings are having to deal with.

Do not keep flushing. Ingoing water ph should be between 6.3 and 6.8ish. How did you determine that your water ph is in the 7.3ish range?

In an emergency, you can use vinegar (works ok for emergencies) or lemon juice (not for long-term use) to lower the ph a tad, but it's best to get some phDown (General Hydroponics) or something similar that's made for lowering botanical ph, for the long-haul. Wait till their next watering to make these adjustments. But nothing I've seen in your seedlings screams "emergency" yet. Relax.