Off to an interesting start. The planet of the grapes is looking good and growing strong. The blueberry muffin on the other hand is not looking as good. Both have been in the same tent from the beginning, both are planted in happy frog soil and have been watered with the same pH water. So I'm kind of confused why one is thriving and the other is struggling. We will see how they look in another week.
I'm kinda having same problem as you atm. What helped was getting a kitchen scale to weigh your medium bag dry then fully saturated and you deduce the water content for a small plant then you can do proper drybacks and maintenane shots as well as how much she transpires once they pick it up. Note that a standard 5Kg scale won't take more than a 2 gallon and you will probably have to make a stand to properly use the scale so check the scale capacity for your medium but if you can calculate water content you'll do better in a smaller bag.🙌