Dolomite lime would help with acidic soil.
Your seedling looks good though, not much sign of a PH problem yet.
Edit:
You don't want to over water them. You can go buy the weight of the container. Try to remember how heavy it was when you watered it, when it feels pretty light it might be a good time to water.
What has worked for me, is. If you stick you finger into the dirt upto the 2nd knuckle, and it doesn't feel very moist on your finger tip. It's probably time to water it.
Over watering can cause a great deal of problems.