Why is this and what can I do to change it?
Just to give you some context mine isn't a typical new tank.
I used Nutri sea live water, wet live rock, live sand, a bottle of Tims. My cycle lasted like two weeks before I was at 0 Ammonia and Nitrites.
I got Pods, bristleworms, fan worms, sponges, snails, hermit crab, all kinds of stuff just thriving in there. Diatom phase is already receding.
Know it's a new tank, but it's got lots for corals to filter feed on in there and I have a bottle of Algaebarn- Copepods/phytoplankton on the way too to add even more biodiversity, which should be well established in the water column by the time I add any coral.