In saltwater, you only need a skimmer, live rock and enough flow in the tank to keep detritus (poop) off the sand/rock so that it can get grabbed by the skimmer or filter sock (if you use one). Ideally you have a sump to put the skimmer in, but a HOB
can work. Regular mechanical filters need to be cleaned weekly to keep the nitrates from elevating quickly. Do partial water changes as frequently as needed to remove nitrates and you are good to go.
Having diatoms in the past is just part of having a new tanks. They feed off of the silicates in the sand, but once that is gone, they have no food source and will die off. Takes a few weeks usually. If it stays longer, it might be algae.