Cycling help

Hey guys new to the hobby and need some direction. I know there are like 10,000 posts on cycling but I need some input. So i started a 15 gallon column tank used a full bag of Caribsea live sand and like 6 pieces of decent sized live rock ( don't know the lbs) set everything and waited 2 weeks testing everyday and saw no sign of ammonia whatsoever. Read on here that sometimes there might not be enough die off on the live rock sometimes to get any ammonia and figured this was the case as I live less than 10 minutes from my LFS. So I put a chunk of raw shrimp in and 2 days later saw a ammonia spike of 2.0 using API test. Next morning started to see diatoms forming on sand. That was 3 days ago. Now my ammonia is down to almost nothing, nitrite is at .5 and nitrite is at 20. And have a super thick layer of diatoms on almost everything except glass and can see little bubbles on the diatoms. Should I remove the shrimp, leave it, start phantom feeding until everything drops? Just wondering what the next action you would take. Also have not done any water changes and used ro/di water at the get go. Will post a pic of what the tank looks like. Thanks in advance guys, this site is amazing.