All good advice here so I won't add much more. Bottom line is that right now your tank is new and in the uglies, so your only focus should be keeping the fish happy, and nutrients in the lower range if possible (to help get you out of the uglies).
Params to focus on for next few months:
-Temp
-Salinity
-Nitrate (and to some degree phosphate, but even this you can pay less attention to for now).
I would also consider doubling your water change schedule. This will help stabilize things for you, and you don't have to worry about corals right now, it's the fish you need to keep happy.
Tips:
-Make sure your change water is exactly right with salinity. Check it twice before making the water change.
-What is the Alk/CA/Mg on your salt mix? This is the number your tank params should be stabilizing towards on its own.
-Figure out the right amount to feed, and feed consistent amount daily. Fish only need enough food to eat for 1-2 min. They have tiny stomaches, but will always seem hungry. If your nitrates continue to go up with that amount of feeding, add another level of filtration to balance (ideally not chemical filtration yet at this point).
-You can check your alk/ca, but don't worry about correcting it yet with dosing. Just keep tabs on it for now, and keep a log. See if water changes are getting you in the right direction.
-Even PH... don't stress too hard. Test the PH of your freshly mixed salt water before a water change. If it's off, go downstream and check your RODI water's PH.
If you do the above, in ~2 months time the uglies will be gone and you'll be ready to start adding some LPS corals and THEN - after a few weeks delay - start researching dosing. Dosing is one of the hardest things for a new reefer to learn how to do, so cut yourself a break.
(I guess I did add advice

. Good luck!