hair algae is a ntrient issue meaning you have excessive nitrates and phosphates in your tank, using a media reactor with gfo will consume your phosphate aggressively, and nitrates are in the water column and pockets can be hidden in live rock and sand so can be manually removed via water changes and good husbandry meaning blow off the rocks with a turkey baster, clean your sand and have ample flow throughout so ditrius doesnt settle in hidden places.cheato by its self will do nothing for your nutrient export it just helps.
using ro water,regular light schedules with bulbs of good age, flow, media reactors,refuge,regular water changes,carbon dosing, low feedings, blotting frozen food,keeping a low bio load,skimmer etc etc etc are all things we use together to control nutrients any of these by them selves dont really do the trick.
diatoms is something that happens in new tanks for the most part, and usually will dissappear once the tank is stabilized, if it becomes really unsightly you can kill your lights and stir it around or brush it off rocks but it will come back but usually dissappears with in a couple weeks if the conditions are right meaning not adding more nutrients to your tank
if this is a new tank i suggest taking it slower and making sure you do some research basically you want to improve water quality before moving any further ahead with fish or corals.
cheers
