That’s great! your off to a wonderful start.
Try not to get caught up in worrying about how big one is to another. It’s quite common to have same seeds that grow different and even look different. I grew two sour diesels last grow in coco and they were totally different when it came time to flower.
It’s not only an experiment but it’s also addictive.
PH should be maintained right around 5.8.
This is what I used. I got it off the GH website. Hopefully it will help. Keep in mind, it’s easier to add nutrients if they are hungry. If you over feed the nute burn will not get better on the leaves that got nute burn.
When you do a runoff, you are testing the PH and the PPM’s. It’ll become vital that you know what’s going in, and what’s coming out later in the grow. That will tell you how much they are eating / drinking. It can also tell you whether or not you have any kind of nutrient lockout.
Have any question, ask away! That’s why we are all here.