I see the biggest problem with people getting in the hobby is they just dont take it slow enough in the beginning. I was the same way years ago when I first got into the fresh water hobby. And there are similarities when it comes to introducing livestock. You dont mention how long you let your tank cycle first. I'd stop adding fish until you get this right. Keep some clean up crew and a couple of damsels for now. change 20% of your water every 2 weeks using a good quality salt. You may have just got off to the wrong start using tap water. Test your nitrites every 2 weeks along with your alk and calcium. when things are stable add some livestock a little at a time and keep monitoring. having a 4 stage ro unit and a good skimmer cleaned every week is important. you'll get it right!