Armin Arlert

that's compacting soil. Happens when to much water is added or not enouth perlite is mixed into the substrate. Can cause more issues down the road. Water slowly and evenly. You can add more soil but if its the same its just going to compact more.

Jist make sure you are slow and steady, think , just make sure not to dump all your water in one go, this can compact the soil and possibly suffocate roots or at least make it more difficult to penetrate and grow. Top it up for sure, won't t harm, best of luck.

Yes you should do that. It makes the irrigation easier, as it prevents the water from running down to the sides of the soil. Dry soil can become quite hydrophobic.... Also it prevents flying insects like fungus gnats from getting deep down into the substrate, which can make it harder to get rid of them. So definitely go for it! Good luck, happy 420!