@GpixL_ , there is no way that your ALK is 16 or 15 if you're using Instant Ocean and it is mixed correctly to a salinity of around 34-35 ppt (1.023-1.027). You really need to take your water to a trusted LFS and have them test it for you. If your LFS is the one trying to sell you a coral with bio-balls instead of cycled live rock, I would avoid that LFS.
Your tank is new, and you have a choice. You can either decide now to be patient and take your time, or you can spend a lot of extra cash chasing problems that are created by rushing.
You do need to keep the surface of the water agitated. High ALK
DOES NOT create oxygen in a system. Surface agitation allows gas exchange in your tank.